perf: Fix argument of perf_arch_fetch_caller_regs

"struct regs" was set to argument of perf_arch_fetch_caller_regs
off-case. It should be "struct pt_regs".

This fixes various build errors in archs that have CONFIG_PERF_EVENTS=y
but no overriden implementation of perf_arch_fetch_caller_regs.

cc1: warnings being treated as errors
In file included from include/linux/ftrace_event.h:8,
                 from include/trace/syscall.h:6,
                 from include/linux/syscalls.h:75,
                 from arch/sh/kernel/sys_sh32.c:9:
include/linux/perf_event.h:937: error: 'struct regs' declared inside parameter list
include/linux/perf_event.h:937: error: its scope is only this definition or declaration, which is probably not what you want
include/linux/perf_event.h: In function 'perf_fetch_caller_regs':
include/linux/perf_event.h:952: error: passing argument 1 of 'perf_arch_fetch_caller_regs' from incompatible pointer type

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: David Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <AANLkTinKKFKEBQrZ3Hkj-XCaMwaTqulb-XnFzqEYiFRr@mail.gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>