drm: Fix return type of crc .poll()

Sparse compains:
../drivers/gpu/drm/drm_debugfs_crc.c:350:17: warning: incorrect type in initializer (different base types)
../drivers/gpu/drm/drm_debugfs_crc.c:350:17:    expected restricted __poll_t ( *poll )( ... )
../drivers/gpu/drm/drm_debugfs_crc.c:350:17:    got unsigned int ( * )( ... )

Change the .poll() return type to __poll_t to silence it.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190710125143.9965-5-ville.syrjala@linux.intel.comReviewed-by: Sean Paul <sean@poorly.run>

drivers/gpu/drm/drm_debugfs_crc.c

@@ -334,19 +334,17 @@ static ssize_t crtc_crc_read(struct file *filep, char __user *user_buf,
 	return LINE_LEN(crc->values_cnt);
 }
 
-static unsigned int crtc_crc_poll(struct file *file, poll_table *wait)
+static __poll_t crtc_crc_poll(struct file *file, poll_table *wait)
 {
 	struct drm_crtc *crtc = file->f_inode->i_private;
 	struct drm_crtc_crc *crc = &crtc->crc;
-	unsigned ret;
+	__poll_t ret = 0;
 
 	poll_wait(file, &crc->wq, wait);
 
 	spin_lock_irq(&crc->lock);
 	if (crc->source && crtc_crc_data_count(crc))
-		ret = POLLIN | POLLRDNORM;
-	else
-		ret = 0;
+		ret |= EPOLLIN | EPOLLRDNORM;
 	spin_unlock_irq(&crc->lock);
 
 	return ret;