ubifs: Fix memory leak in lprobs self-check

commit eef19816ada3abd56d9f20c88794cc2fea83ebb2 upstream.

Allocate the buffer after we return early.
Otherwise memory is being leaked.

Cc: <stable@vger.kernel.org>
Fixes: 1e51764a ("UBIFS: add new flash file system")
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>