makepkg: fix regression in split package function checking

Commit 13748ca052 inversed the nature of one test wherein the if clause would
throw a fatal error if a legitimate package function was defined in PKGBUILD.

Signed-off-by: Andres P <aepd87@gmail.com>
Signed-off-by: Allan McRae <allan@archlinux.org>
Signed-off-by: Dan McGee <dan@archlinux.org>

scripts/makepkg.sh.in

@@ -1255,7 +1255,7 @@ check_sanity() {
 
 	if (( ${#pkgname[@]} > 1 )); then
 		for pkg in ${pkgname[@]}; do
-			if declare -f package_${pkg} >/dev/null; then
+			if ! declare -f package_${pkg} >/dev/null; then
 				error "$(gettext "missing package function for split package '%s'")" "$pkg"
 				return 1
 			fi