drm/radeon: remove set but not used variable 'size', 'relocs_chunk'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/radeon/r600_cs.c: In function r600_cs_track_validate_cb:
drivers/gpu/drm/radeon/r600_cs.c:353:22: warning: variable size set but not used [-Wunused-but-set-variable]
drivers/gpu/drm/radeon/r600_cs.c: In function r600_cs_track_validate_db:
drivers/gpu/drm/radeon/r600_cs.c:520:27: warning: variable size set but not used [-Wunused-but-set-variable]
drivers/gpu/drm/radeon/r600_cs.c: In function r600_dma_cs_next_reloc:
drivers/gpu/drm/radeon/r600_cs.c:2345:26: warning: variable relocs_chunk set but not used [-Wunused-but-set-variable]

The first 'size' is not used since commit f30df2fa ("drm/radeon/r600:
fix tiling issues in CS checker.")

The second 'size' is introduced by commit 88f50c80 ("drm/radeon/kms:
add htile support to the cs checker v3"), but never used, so remove it.

'relocs_chunk' is not used since commit 9305ede6 ("radeon/kms:
fix dma relocation checking")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>