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

In the Linux kernel, the following vulnerability has been resolved:

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.

(cherry picked from commit 2d52de55f9ee7aaee0e09ac443f77855989c6b68)