staging/lustre: Only set INTERRUPTIBLE state before calling schedule

In __l_wait_event the condition could be a complicated function that does
allocations and other potentialy blocking activities, so it sohuld
not be called in a task state other than RUNNABLE

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>