termux_step_create_datatar.sh: add data/ to tar instead of ./

This avoids "./" being part of the tar. "./" translates to the
systemroot / when we extract, and this is problematic since tar cannot
change permissions and ownerships of this folder. tar 1.34 gives an
error:

    tar: .: Cannot change mode to rwxr-xr-x: Operation not permitted
    tar: Exiting with failure status due to previous errors

when we try to extract the data.tar.xz.

scripts/build/termux_step_create_datatar.sh

@@ -4,5 +4,5 @@ termux_step_create_datatar() {
 		rm -rf data
 	fi
 
-	tar -cJf "$TERMUX_PKG_PACKAGEDIR/data.tar.xz" -H gnu .
+	tar -cJf "$TERMUX_PKG_PACKAGEDIR/data.tar.xz" -H gnu data
 }