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

 drivers/gpu/drm/radeon/radeon_vm.c:131: warning: Function parameter or member 'rdev' not described in 'radeon_vm_get_bos'
 drivers/gpu/drm/radeon/radeon_vm.c:643: warning: Excess function parameter 'start' description in 'radeon_vm_update_page_directory'
 drivers/gpu/drm/radeon/radeon_vm.c:643: warning: Excess function parameter 'end' description in 'radeon_vm_update_page_directory'
 drivers/gpu/drm/radeon/radeon_vm.c:819: warning: Function parameter or member 'ib' not described in 'radeon_vm_update_ptes'
 drivers/gpu/drm/radeon/radeon_vm.c:915: warning: Function parameter or member 'bo_va' not described in 'radeon_vm_bo_update'
 drivers/gpu/drm/radeon/radeon_vm.c:915: warning: Excess function parameter 'vm' description in 'radeon_vm_bo_update'
 drivers/gpu/drm/radeon/radeon_vm.c:915: warning: Excess function parameter 'bo' description in 'radeon_vm_bo_update'
 drivers/gpu/drm/radeon/radeon_vm.c:1155: warning: Excess function parameter 'vm' description in 'radeon_vm_bo_invalidate'

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>