perf dwarf: Fix potential array out of bounds access

There is a problem in the dwarf-regs.c files for sh, sparc and x86 where
it is possible to make an out-of-bounds array access when searching for
register names.

This patch fixes it by replacing '<=' to '<', so when register (number
== XXX_MAX_REGS), get_arch_regstr() will return NULL.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Reviewed-by: Matt Fleming <matt@console-pimps.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@huawei.com
Link: http://lkml.kernel.org/r/1441078184-105038-1-git-send-email-wangnan0@huawei.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>