drm/vmwgfx: Fix a buffer object leak

commit 13f149d47392782baafd96d54d4e65f3b5ca342f upstream.

A buffer object leak was introduced when fixing a premature buffer
object release. Fix this.

Cc: <stable@vger.kernel.org>
Fixes: 73a88250b709 ("Fix a destoy-while-held mutex problem.")
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>