drm_rmmap_ioctl(): remove dead code

This patch removes some obviously dead code spotted by the Coverity
checker.
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/drm/drm_bufs.c

@@ -479,11 +479,6 @@ int drm_rmmap_ioctl(struct inode *inode, struct file *filp,
 		return -EINVAL;
 	}
 
-	if (!map) {
-		mutex_unlock(&dev->struct_mutex);
-		return -EINVAL;
-	}
-
 	/* Register and framebuffer maps are permanent */
 	if ((map->type == _DRM_REGISTERS) || (map->type == _DRM_FRAME_BUFFER)) {
 		mutex_unlock(&dev->struct_mutex);