drm/radeon/kms: Do not unpin buffer in fb destruction

It's not necessary to unpin buffer in fb destruction. pin/unpin
need to be balanced and we don't pin in fb creation. We pin when
an fb is associated to a crtc and unpin when the fb is disassociated
from the crtc.

Note:
Maybe we should take reference on fb in set_base callback so fb
doesn't disappear until it's unbind from ctrc.
Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_display.c

@@ -668,7 +668,6 @@ static void radeon_user_framebuffer_destroy(struct drm_framebuffer *fb)
 		radeonfb_remove(dev, fb);
 
 	if (radeon_fb->obj) {
-		radeon_gem_object_unpin(radeon_fb->obj);
 		mutex_lock(&dev->struct_mutex);
 		drm_gem_object_unreference(radeon_fb->obj);
 		mutex_unlock(&dev->struct_mutex);