powerpc/kprobes: Have optimized_callback() use preempt_enable()

powerpc/kprobes: Have optimized_callback() use preempt_enable()

Similar to x86 commit 2e62024c265aa6 ("kprobes/x86: Use preempt_enable()
in optimized_callback()"), change powerpc optprobes to use
preempt_enable() rather than preempt_enable_no_resched() since powerpc
also removed irq disabling for optprobes in commit f72180cc93a2c6
("powerpc/kprobes: Do not disable interrupts for optprobes and
kprobes_on_ftrace").

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/1885bab182626c33d9bf6421f430abf924c521a5.1666262278.git.naveen.n.rao@linux.vnet.ibm.com