drm/nouveau: Fix crtc->primary->fb vs. drm_fb fail

So it looks like the code is trying to pick between the passed in fb and
crtc->primary->fb based on that funky 'bool atomic'. But later it will
mix uses of both drm_fb (which was picked by the aforementioned logic)
and crtc->primary->fb. So looks like a bug to me. Let's make it use
drm_fb only.

Cc: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1479498793-31021-11-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

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

@@ -854,9 +854,9 @@ nv04_crtc_do_mode_set_base(struct drm_crtc *crtc,
 
 	/* Update the framebuffer format. */
 	regp->CRTC[NV_CIO_CRE_PIXEL_INDEX] &= ~3;
-	regp->CRTC[NV_CIO_CRE_PIXEL_INDEX] |= (crtc->primary->fb->depth + 1) / 8;
+	regp->CRTC[NV_CIO_CRE_PIXEL_INDEX] |= (drm_fb->depth + 1) / 8;
 	regp->ramdac_gen_ctrl &= ~NV_PRAMDAC_GENERAL_CONTROL_ALT_MODE_SEL;
-	if (crtc->primary->fb->depth == 16)
+	if (drm_fb->depth == 16)
 		regp->ramdac_gen_ctrl |= NV_PRAMDAC_GENERAL_CONTROL_ALT_MODE_SEL;
 	crtc_wr_cio_state(crtc, regp, NV_CIO_CRE_PIXEL_INDEX);
 	NVWriteRAMDAC(dev, nv_crtc->index, NV_PRAMDAC_GENERAL_CONTROL,