drm/radeon/r600_cs: Fix possible int overflow in r600_packet3_check()

It is possible, although unlikely, that an integer overflow will occur
when the result of radeon_get_ib_value() is shifted to the left.

Avoid it by casting one of the operands to larger data type (u64).

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

Signed-off-by: Igor Artemiev <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/radeon/r600_cs.c

···
 				return -EINVAL;
 			}
 
-			offset = radeon_get_ib_value(p, idx+1) << 8;
+			offset = (u64)radeon_get_ib_value(p, idx+1) << 8;
 			if (offset != track->vgt_strmout_bo_offset[idx_value]) {
 				DRM_ERROR("bad STRMOUT_BASE_UPDATE, bo offset does not match: 0x%llx, 0x%x\n",
 					  offset, track->vgt_strmout_bo_offset[idx_value]);