mm/z3fold.c: do not include rwlock.h directly

rwlock.h should not be included directly. Instead linux/splinlock.h
should be included. One thing it does is to break the RT build.

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20200224133631.1510569-1-bigeasy@linutronix.de


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>