[Build-Pkg] Fixed to pass -o when mounting tmpfs only if $SDECFG_SRC_TMPFS_OPT is set

scripts/Build-Pkg

@@ -496,7 +496,7 @@ echo_status "Preparing build in src.$pkg.$config.$id"
 if [ $clear_src = 1 ] ; then
 	mkdir -p $builddir; chmod 0755 $builddir
 	if [ "$SDECFG_SRC_TMPFS" = 1 ]; then
-		mount -t tmpfs -n -o $SDECFG_SRC_TMPFS_OPT none $builddir
+		mount -t tmpfs -n ${SDECFG_SRC_TMPFS_OPT:+-o $SDECFG_SRC_TMPFS_OPT} none $builddir
 	fi
 else
 	mkdir -p $builddir; chmod 0755 $builddir