drm/amd/amdgpu/amdgpu_gmc: Fix a little naming related doc-rot

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

 drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c:487: warning: expecting prototype for amdgpu_tmz_set(). Prototype was for amdgpu_gmc_tmz_set() instead
 drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c:533: warning: expecting prototype for amdgpu_noretry_set(). Prototype was for amdgpu_gmc_noretry_set() instead

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>