drm_mode_create_lease_ioctl(): fix open-coded filp_clone_open()

Failure of ->open() should *not* be followed by fput().  Fixed by
using filp_clone_open(), which gets the cleanups right.

Cc: stable@vger.kernel.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>