markup_oops.pl: fix $func_offset error with x86_64

When I use markup_oops.pl parse a x8664 oops, I got:

objdump: --start-address: bad number: NaN
No matching code found
This is because:
main::(./m.pl:228): open(FILE, "objdump -dS --adjust-vma=$vmaoffset --start-address=$decodestart --stop-address=$decodestop $filename |") || die "Cannot start objdump";
DB<3> p $decodestart
NaN

This NaN is from:
main::(./m.pl:176): my $decodestart = Math::BigInt->from_hex("0x$target") - Math::BigInt->from_hex("0x$func_offset");
DB<2> p $func_offset
0x175

There is already a "0x" in $func_offset, another 0x makes it a NaN.

The $func_offset is from line:

if ($line =~ /RIP: 0010:\[\<[0-9a-f]+\>\] \[\<[0-9a-f]+\>\] ([a-zA-Z0-9\_]+)\+(0x[0-9a-f]+)\/0x[a-f0-9]/) {
$function = $1;
$func_offset = $2;
}

I make a patch to change "(0x[0-9a-f]+)\/0x[a-f0-9]/)" to "0x([0-9a-f]+)\/0x[a-f0-9]/)".

Signed-off-by: Hui Zhu <teawater@gmail.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>