[S390] sclp: don't call local_bh_disable/_local_bh_enable if in_interrupt()

local_bh_disable/_local_bh_enable must not be called if in_irq() is
true. Besides that if in_interrupt() is true bottom halves are
disabled anyway.

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