drm/amd/amdxcp: Fix warnings

Range of possible values of pdev_num is 0-63. Use int8_t as data type.
That also fixes below warnings:

>> drivers/gpu/drm/amd/amdxcp/amdgpu_xcp_drv.c:59:58: warning: '%d'
>> directive output may be truncated writing between 1 and 11 bytes into
>> a region of size 9 [-Wformat-truncation=]
59 | snprintf(dev_name, sizeof(dev_name), "amdgpu_xcp_%d", pdev_num);
| ^~
drivers/gpu/drm/amd/amdxcp/amdgpu_xcp_drv.c:59:46: note: directive argument in the range [-2147483648, 63]
59 | snprintf(dev_name, sizeof(dev_name), "amdgpu_xcp_%d", pdev_num);
| ^~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdxcp/amdgpu_xcp_drv.c:59:9: note: 'snprintf' output between 13 and 23 bytes into a destination of size 20
59 | snprintf(dev_name, sizeof(dev_name), "amdgpu_xcp_%d", pdev_num);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: 97d814fe4f69 ("drm/amd/amdxcp: Use unique name for partition dev")
Signed-off-by: Lijo Lazar <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Reviewed-by: Hawking Zhang <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdxcp/amdgpu_xcp_drv.c

···
 	.minor = 0,
 };
 
-static int pdev_num;
+static int8_t pdev_num;
 static struct xcp_device *xcp_dev[MAX_XCP_PLATFORM_DEVICE];
 
 int amdgpu_xcp_drm_dev_alloc(struct drm_device **ddev)