drm/radeon/r600_cs: Build failures with GCC 16

[Brahmajit Das]

Hello Developers,

Building linux-next with GCC 16 results in this following build error

$ make
  CALL    scripts/checksyscalls.sh
  DESCEND objtool
  INSTALL libsubcmd_headers
  CC      drivers/gpu/drm/radeon/r600_cs.o
drivers/gpu/drm/radeon/r600_cs.c: In function ‘r600_texture_size’:
drivers/gpu/drm/radeon/r600_cs.c:1411:29: error: variable ‘level’ set but not used [-Werror=unused-but-set-variable=]
 1411 |         unsigned offset, i, level;
      |                             ^~~~~
cc1: all warnings being treated as errors
make[6]: *** [scripts/Makefile.build:287: drivers/gpu/drm/radeon/r600_cs.o] Error 1
make[5]: *** [scripts/Makefile.build:556: drivers/gpu/drm/radeon] Error 2
make[4]: *** [scripts/Makefile.build:556: drivers/gpu/drm] Error 2
make[3]: *** [scripts/Makefile.build:556: drivers/gpu] Error 2
make[2]: *** [scripts/Makefile.build:556: drivers] Error 2
make[1]: *** [/home/listout/linux/Makefile:2011: .] Error 2
make: *** [Makefile:248: __sub-make] Error 2

I'm not sure whether this is kernel bug or GCC bug at the moment. But
building with GCC 15 does not give this error, hence I'm more inclined
towards the latter.
Planning to also report this on GCC side, wanted to get some
opinion/feedback from kernel devs as well.
I'm on GCC 16.0.0_p2025080.

-- 
Regards,
listout