drm/amdgpu: Fix buffer size to prevent truncation in gfx_v12_0_init_microcode

This commit fixes multiple potential truncations when writing the
strings _pfp.bin, _me.bin, _rlc.bin, and _mec.bin into the fw_name
buffer in the gfx_v12_0_init_microcode function in the gfx_v12_0.c file

The ucode_prefix size was reduced from 30 to 15 to ensure the snprintf
function does not exceed the size of the fw_name buffer.

Thus fixing the below with gcc W=1:
drivers/gpu/drm/amd/amdgpu/gfx_v12_0.c: In function ‘gfx_v12_0_early_init’:
drivers/gpu/drm/amd/amdgpu/gfx_v12_0.c:421:54: warning: ‘_pfp.bin’ directive output may be truncated writing 8 bytes into a region of size between 4 and 33 [-Wformat-truncation=]
421 | snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_pfp.bin", ucode_prefix);
| ^~~~~~~~
drivers/gpu/drm/amd/amdgpu/gfx_v12_0.c:421:9: note: ‘snprintf’ output between 16 and 45 bytes into a destination of size 40
421 | snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_pfp.bin", ucode_prefix);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/gfx_v12_0.c:428:54: warning: ‘_me.bin’ directive output may be truncated writing 7 bytes into a region of size between 4 and 33 [-Wformat-truncation=]
428 | snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_me.bin", ucode_prefix);
| ^~~~~~~
drivers/gpu/drm/amd/amdgpu/gfx_v12_0.c:428:9: note: ‘snprintf’ output between 15 and 44 bytes into a destination of size 40
428 | snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_me.bin", ucode_prefix);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/gfx_v12_0.c:436:62: warning: ‘_rlc.bin’ directive output may be truncated writing 8 bytes into a region of size between 4 and 33 [-Wformat-truncation=]
436 | snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_rlc.bin", ucode_prefix);
| ^~~~~~~~
drivers/gpu/drm/amd/amdgpu/gfx_v12_0.c:436:17: note: ‘snprintf’ output between 16 and 45 bytes into a destination of size 40
436 | snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_rlc.bin", ucode_prefix);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/gfx_v12_0.c:448:54: warning: ‘_mec.bin’ directive output may be truncated writing 8 bytes into a region of size between 4 and 33 [-Wformat-truncation=]
448 | snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_mec.bin", ucode_prefix);
| ^~~~~~~~
drivers/gpu/drm/amd/amdgpu/gfx_v12_0.c:448:9: note: ‘snprintf’ output between 16 and 45 bytes into a destination of size 40
448 | snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_mec.bin", ucode_prefix);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Cc: Lijo Lazar <[e-mail]>
Cc: Christian König <[e-mail]>
Cc: Alex Deucher <[e-mail]>
Signed-off-by: Srinivasan Shanmugam <[e-mail]>
Reviewed-by: Lijo Lazar <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/gfx_v12_0.c

···
 static int gfx_v12_0_init_microcode(struct amdgpu_device *adev)
 {
 	char fw_name[40];
-	char ucode_prefix[30];
+	char ucode_prefix[15];
 	int err;
 	const struct rlc_firmware_header_v2_0 *rlc_hdr;
 	uint16_t version_major;