drm/radeon/kms: remove set but not used variable 'pll'

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

drivers/gpu/drm/radeon/radeon_legacy_tv.c: In function 'radeon_legacy_tv_init_restarts':
drivers/gpu/drm/radeon/radeon_legacy_tv.c:435:21: warning:
 variable 'pll' set but not used [-Wunused-but-set-variable]
  struct radeon_pll *pll;

It never used since introduction in commit
4ce001ab ("drm/radeon/kms: add initial radeon tv-out support.")
Also remove related variables 'dev, rdev, radeon_crtc'

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>