drm/crtc: constify drm_crtc_mask parameter

Now that drm_crtc_index takes a const, the same can be done for drm_crtc_mask.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/6e32d013-6fee-34ad-f8d2-59139f3dc4c1@linux.intel.com

include/drm/drm_crtc.h

@@ -1359,7 +1359,7 @@ static inline unsigned int drm_crtc_index(const struct drm_crtc *crtc)
  * Given a registered CRTC, return the mask bit of that CRTC for an
  * encoder's possible_crtcs field.
  */
-static inline uint32_t drm_crtc_mask(struct drm_crtc *crtc)
+static inline uint32_t drm_crtc_mask(const struct drm_crtc *crtc)
 {
 	return 1 << drm_crtc_index(crtc);
 }

include/drm/drm_encoder.h

@@ -189,7 +189,7 @@ static inline unsigned int drm_encoder_index(struct drm_encoder *encoder)
 }
 
 /* FIXME: We have an include file mess still, drm_crtc.h needs untangling. */
-static inline uint32_t drm_crtc_mask(struct drm_crtc *crtc);
+static inline uint32_t drm_crtc_mask(const struct drm_crtc *crtc);
 
 /**
  * drm_encoder_crtc_ok - can a given crtc drive a given encoder?