drm/radeon: fix uninitialized size issue in radeon_vce_cs_parse()

On the off chance that command stream passed from userspace via
ioctl() call to radeon_vce_cs_parse() is weirdly crafted and
first command to execute is to encode (case 0x03000001), the function
in question will attempt to call radeon_vce_cs_reloc() with size
argument that has not been properly initialized. Specifically, 'size'
will point to 'tmp' variable before the latter had a chance to be
assigned any value.

Play it safe and init 'tmp' with 0, thus ensuring that
radeon_vce_cs_reloc() will catch an early error in cases like these.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: 2fc5703abda2 ("drm/radeon: check VCE relocation buffer range v3")
Signed-off-by: Nikita Zhandarovich <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>
(cherry picked from commit 2d52de55f9ee7aaee0e09ac443f77855989c6b68)
Cc: [e-mail]

drivers/gpu/drm/radeon/radeon_vce.c

···
 {
 	int session_idx = -1;
 	bool destroyed = false, created = false, allocated = false;
-	uint32_t tmp, handle = 0;
+	uint32_t tmp = 0, handle = 0;
 	uint32_t *size = &tmp;
 	int i, r = 0;