base-files: upgrade: fix initramfs detection

Commit "initramfs: switch to tmpfs to fix ujail" switched initramfs to
now use tmpfs, it causes $(rootfs_type) to now return tmpfs when
running initramfs image instead of being empty.

This broke initramfs detection which prevents config files from
being saved as it does not work from initramfs.

So, lets test for $(rootfs_type) returning "tmpfs" instead.

Fixes: 7fd3c68 ("initramfs: switch to tmpfs to fix ujail)

Signed-off-by: Robert Marko <robimarko@gmail.com>

package/base-files/Makefile

@@ -12,7 +12,7 @@ include $(INCLUDE_DIR)/version.mk
 include $(INCLUDE_DIR)/feeds.mk
 
 PKG_NAME:=base-files
-PKG_RELEASE:=240
+PKG_RELEASE:=241
 PKG_FLAGS:=nonshared
 
 PKG_FILE_DEPENDS:=$(PLATFORM_DIR)/ $(GENERIC_PLATFORM_DIR)/base-files/

package/base-files/files/sbin/sysupgrade

@@ -216,7 +216,7 @@ include /lib/upgrade
 do_save_conffiles() {
 	local conf_tar="$1"
 
-	[ -z "$(rootfs_type)" ] && {
+	[ "$(rootfs_type)" = "tmpfs" ] && {
 		echo "Cannot save config while running from ramdisk." >&2
 		ask_bool 0 "Abort" && exit
 		rm -f "$conf_tar"