scripts/portable_date.sh: fix parsing of date strings on non-GNU systems

Signed-off-by: Felix Fietkau <[email protected]>

SVN-Revision: 48592

scripts/portable_date.sh

@@ -2,10 +2,10 @@
 
 case $(uname) in
 	NetBSD|OpenBSD|DragonFly|FreeBSD|Darwin)
-		date -r $1 $2
+		date -j -f "%Y-%m-%d %H:%M:%S %z" "$1" "$2" 2>/dev/null
 		;;
 	*)
-		date -d @$1 $2
+		date -d "@$1" "$2"
 esac
 
 exit $?