powerpc/kprobes: Remove duplicate saving of MSR

set_current_kprobe() already saves regs->msr into kprobe_saved_msr. Remove the
redundant save.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>