checkstack: fix printed address

All addresses printed by checkstack have an extra incorrect 0 appended at
the end.

This was introduced with commit 677f1410 ("scripts/checkstack.pl: don't
display $dre as different entity"): since then the address is taken from
the line which contains the function name, instead of the line which
contains stack consumption. E.g. on s390:

0000000000100a30 <do_one_initcall>:
...
  100a44:       e3 f0 ff 70 ff 71       lay     %r15,-144(%r15)

So the used regex which matches spaces and hexadecimal numbers to extract
an address now matches a different substring. Subsequently replacing spaces
with 0 appends a zero at the and, instead of replacing leading spaces.

Fix this by using the proper regex, and simplify the code a bit.

Link: https://lkml.kernel.org/r/20231120183719.2188479-2-hca@linux.ibm.com
Fixes: 677f1410

 ("scripts/checkstack.pl: don't display $dre as different entity")
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Cc: Maninder Singh <maninder1.s@samsung.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Vaneet Narang <v.narang@samsung.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>