GPU-DRM-Radeon: Delete an unnecessary check before drm_gem_object_unreference_unlocked()

The drm_gem_object_unreference_unlocked() function tests whether
its argument is NULL and then returns immediately.
Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.
Signed-off-by: NMarkus Elfring <elfring@users.sourceforge.net>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_display.c

@@ -1324,9 +1324,7 @@ static void radeon_user_framebuffer_destroy(struct drm_framebuffer *fb)
 {
 	struct radeon_framebuffer *radeon_fb = to_radeon_framebuffer(fb);
 
-	if (radeon_fb->obj) {
-		drm_gem_object_unreference_unlocked(radeon_fb->obj);
-	}
+	drm_gem_object_unreference_unlocked(radeon_fb->obj);
 	drm_framebuffer_cleanup(fb);
 	kfree(radeon_fb);
 }