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

 drivers/gpu/drm/radeon/radeon_irq_kms.c:56: warning: Function parameter or member 'irq' not described in 'radeon_driver_irq_handler_kms'
 drivers/gpu/drm/radeon/radeon_irq_kms.c:56: warning: Function parameter or member 'arg' not described in 'radeon_driver_irq_handler_kms'
 drivers/gpu/drm/radeon/radeon_irq_kms.c:571: warning: Function parameter or member 'n' not described in 'radeon_irq_kms_set_irq_n_enabled'
 drivers/gpu/drm/radeon/radeon_irq_kms.c:571: warning: Excess function parameter 'num' description in 'radeon_irq_kms_set_irq_n_enabled'

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>