Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/radeon/cik.c:1868:5: warning: no previous prototype for ‘ci_mc_load_microcode’ [-Wmissing-prototypes]
 1868 | int ci_mc_load_microcode(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/cik.c:5847:6: warning: no previous prototype for ‘cik_enter_rlc_safe_mode’ [-Wmissing-prototypes]
 5847 | void cik_enter_rlc_safe_mode(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/cik.c:5868:6: warning: no previous prototype for ‘cik_exit_rlc_safe_mode’ [-Wmissing-prototypes]
 5868 | void cik_exit_rlc_safe_mode(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/cik.c:6286:6: warning: no previous prototype for ‘cik_update_cg’ [-Wmissing-prototypes]
 6286 | void cik_update_cg(struct radeon_device *rdev,
 | ^~~~~~~~~~~~~

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>