modpost: fix removing numeric suffixes

With the `-z unique-symbol` linker flag or any similar mechanism,
it is possible to trigger the following:

ERROR: modpost: "param_set_uint.0" [vmlinux] is a static EXPORT_SYMBOL

The reason is that for now the condition from remove_dot():

if (m && (s[n + m] == '.' || s[n + m] == 0))

which was designed to test if it's a dot or a '\0' after the suffix
is never satisfied.
This is due to that `s[n + m]` always points to the last digit of a
numeric suffix, not on the symbol next to it (from a custom debug
print added to modpost):

param_set_uint.0, s[n + m] is '0', s[n + m + 1] is '\0'

So it's off-by-one and was like that since 2014.

Fix this for the sake of any potential upcoming features, but don't
bother stable-backporting, as it's well hidden -- apart from that
LD flag, it can be triggered only with GCC LTO which never landed
upstream.

Fixes: fcd38ed0ff ("scripts: modpost: fix compilation warning")
Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/mod/modpost.c

@@ -1906,7 +1906,7 @@ static char *remove_dot(char *s)
 
 	if (n && s[n]) {
 		size_t m = strspn(s + n + 1, "0123456789");
-		if (m && (s[n + m] == '.' || s[n + m] == 0))
+		if (m && (s[n + m + 1] == '.' || s[n + m + 1] == 0))
 			s[n] = 0;
 
 		/* strip trailing .prelink */