fs/befs/linuxvfs.c: move useless assignment

Control is transfered to unacquire_none when sb->s_fs_info is equal to
NULL, so the assignment to NULL is useless and it is moved above
unacquire_none.

Link: http://lkml.kernel.org/r/ed41da113fc693c7daa4e8813ca04cc766ddfc05.1464226521.git.salah.triki@acm.org


Signed-off-by: Salah Triki <salah.triki@acm.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>