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

 drivers/gpu/drm/radeon/radeon_display.c:264: warning: Function parameter or member '__work' not described in 'radeon_unpin_work_func'
 drivers/gpu/drm/radeon/radeon_display.c:406: warning: Function parameter or member '__work' not described in 'radeon_flip_work_func'
 drivers/gpu/drm/radeon/radeon_display.c:956: warning: Function parameter or member 'freq' not described in 'radeon_compute_pll_avivo'
 drivers/gpu/drm/radeon/radeon_display.c:956: warning: Function parameter or member 'fb_div_p' not described in 'radeon_compute_pll_avivo'
 drivers/gpu/drm/radeon/radeon_display.c:956: warning: Function parameter or member 'frac_fb_div_p' not described in 'radeon_compute_pll_avivo'
 drivers/gpu/drm/radeon/radeon_display.c:956: warning: Function parameter or member 'ref_div_p' not described in 'radeon_compute_pll_avivo'
 drivers/gpu/drm/radeon/radeon_display.c:956: warning: Function parameter or member 'post_div_p' not described in 'radeon_compute_pll_avivo'

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: Sumit Semwal <sumit.semwal@linaro.org>
Cc: report to <xorg-driver-ati@lists.x.org>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>