drm: tegra: use crtc helper drm_crtc_from_index()

Function tegra_crtc_from_pipe() does the exactly same thing as what
crtc helper drm_crtc_from_index() provides.  Use the helper to save
some code.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1483961145-18453-6-git-send-email-shawnguo@kernel.org

drivers/gpu/drm/tegra/drm.c

@@ -804,23 +804,10 @@ static const struct file_operations tegra_drm_fops = {
 	.llseek = noop_llseek,
 };
 
-static struct drm_crtc *tegra_crtc_from_pipe(struct drm_device *drm,
-					     unsigned int pipe)
-{
-	struct drm_crtc *crtc;
-
-	list_for_each_entry(crtc, &drm->mode_config.crtc_list, head) {
-		if (pipe == drm_crtc_index(crtc))
-			return crtc;
-	}
-
-	return NULL;
-}
-
 static u32 tegra_drm_get_vblank_counter(struct drm_device *drm,
 					unsigned int pipe)
 {
-	struct drm_crtc *crtc = tegra_crtc_from_pipe(drm, pipe);
+	struct drm_crtc *crtc = drm_crtc_from_index(drm, pipe);
 	struct tegra_dc *dc = to_tegra_dc(crtc);
 
 	if (!crtc)
@@ -831,7 +818,7 @@ static u32 tegra_drm_get_vblank_counter(struct drm_device *drm,
 
 static int tegra_drm_enable_vblank(struct drm_device *drm, unsigned int pipe)
 {
-	struct drm_crtc *crtc = tegra_crtc_from_pipe(drm, pipe);
+	struct drm_crtc *crtc = drm_crtc_from_index(drm, pipe);
 	struct tegra_dc *dc = to_tegra_dc(crtc);
 
 	if (!crtc)
@@ -844,7 +831,7 @@ static int tegra_drm_enable_vblank(struct drm_device *drm, unsigned int pipe)
 
 static void tegra_drm_disable_vblank(struct drm_device *drm, unsigned int pipe)
 {
-	struct drm_crtc *crtc = tegra_crtc_from_pipe(drm, pipe);
+	struct drm_crtc *crtc = drm_crtc_from_index(drm, pipe);
 	struct tegra_dc *dc = to_tegra_dc(crtc);
 
 	if (crtc)