drm/nouveau: Add local 'fb' variables

Add a local 'fb' variable to a few places to get rid of the
'crtc->primary->fb' stuff. Looks neater and helps me with my poor
coccinelle skills later.

Cc: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1479498793-31021-12-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/nouveau/dispnv04/dfp.c

@@ -290,6 +290,7 @@ static void nv04_dfp_mode_set(struct drm_encoder *encoder,
 	struct nouveau_encoder *nv_encoder = nouveau_encoder(encoder);
 	struct drm_display_mode *output_mode = &nv_encoder->mode;
 	struct drm_connector *connector = &nv_connector->base;
+	const struct drm_framebuffer *fb = encoder->crtc->primary->fb;
 	uint32_t mode_ratio, panel_ratio;
 
 	NV_DEBUG(drm, "Output mode on CRTC %d:\n", nv_crtc->index);
@@ -415,7 +416,7 @@ static void nv04_dfp_mode_set(struct drm_encoder *encoder,
 	/* Output property. */
 	if ((nv_connector->dithering_mode == DITHERING_MODE_ON) ||
 	    (nv_connector->dithering_mode == DITHERING_MODE_AUTO &&
-	     encoder->crtc->primary->fb->depth > connector->display_info.bpc * 3)) {
+	     fb->depth > connector->display_info.bpc * 3)) {
 		if (drm->device.info.chipset == 0x11)
 			regp->dither = savep->dither | 0x00010000;
 		else {