s390/ftrace: remove preempt_disable()/preempt_enable() pair

s390/ftrace: remove preempt_disable()/preempt_enable() pair

It looks like commit 86b3e969188076a5 ("ftrace: disable preemption
when recursion locked") missed a spot in kprobe_ftrace_handler() in
arch/s390/kernel/ftrace.c.
Remove the superfluous preempt_disable/enable_notrace() there too.

Fixes: 86b3e969188076a5 ("ftrace: disable preemption when recursion locked")
Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Link: https://lore.kernel.org/r/20211208151503.1510381-1-jmarchan@redhat.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>