remote.c: spell __attribute__ correctly

We want to tell the compiler that error_buf() uses
printf()-style arguments via the __attribute__ mechanism,
but the original commit (3a429d0), forgot the trailing "__".
This happens to work with real GNUC-compatible compilers
like gcc and clang, but confuses our fallback macro in
git-compat-util.h, which only matches the official name (and
thus the build fails on compilers like Visual Studio).

Reported-by: Philip Oakley <philipoakley@iee.org>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: peff

remote.c

@@ -1705,7 +1705,7 @@ int branch_merge_matches(struct branch *branch,
 	return refname_match(branch->merge[i]->src, refname);
 }
 
-__attribute((format (printf,2,3)))
+__attribute__((format (printf,2,3)))
 static const char *error_buf(struct strbuf *err, const char *fmt, ...)
 {
 	if (err) {