s390/spinlock: fix indentation

checkpatch:
    WARNING: Statements should start on a tabstop
    #9499: FILE: arch/s390/lib/spinlock.c:231:
    +                          return;

sparse:
arch/s390/lib/spinlock.c:81 arch_load_niai4()
    warn: inconsistent indenting

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>