powerpc/kprobes: Remove preempt disable around call to get_kprobe() in arch_prepare_k...

powerpc/kprobes: Remove preempt disable around call to get_kprobe() in arch_prepare_kprobe()

arch_prepare_kprobe() is called from register_kprobe() via
prepare_kprobe(), or through register_aggr_kprobe(), both with the
kprobe_mutex held. Per the comment for get_kprobe():
  /*
   * This routine is called either:
   *	- under the 'kprobe_mutex' - during kprobe_[un]register().
   *				OR
   *	- with preemption disabled - from architecture specific code.
   */

As such, there is no need to disable preemption around the call to
get_kprobe(). Drop the same.

Reported-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1043d06a0affed83a4a46dd29466e72820ee215d.1666262278.git.naveen.n.rao@linux.vnet.ibm.com