config.c: mark file-local function static

Commit 7192777 refactors git_parse_ulong, which is public, into a more
generic function.  But since we kept the git_parse_ulong wrapper, only
that part needs to be public; nobody outside the file calls the
lower-level git_parse_unsigned.

Noticed with sparse.  ("'git_parse_unsigned' was not declared. Should
it be static?")

Signed-off-by: Ramsay Jones <[email protected]>
Explained-by: Jeff King <[email protected]>
Signed-off-by: Jonathan Nieder <[email protected]>

Author: Ramsay Jones

config.c

@@ -498,7 +498,7 @@ static int git_parse_signed(const char *value, intmax_t *ret, intmax_t max)
 	return 0;
 }
 
-int git_parse_unsigned(const char *value, uintmax_t *ret, uintmax_t max)
+static int git_parse_unsigned(const char *value, uintmax_t *ret, uintmax_t max)
 {
 	if (value && *value) {
 		char *end;