treewide: 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 is required so that when installing
on MikroTik devices firmware partition would first get erased fully
before writing.

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

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

Signed-off-by: Robert Marko <[email protected]>

target/linux/ath79/mikrotik/base-files/lib/upgrade/platform.sh

@@ -39,7 +39,7 @@ platform_do_upgrade() {
 		;;
 	*)
 		# NOR devices: erase firmware if booted from initramfs
-		[ -z "$(rootfs_type)" ] && mtd erase firmware
+		[ "$(rootfs_type)" = "tmpfs" ] && mtd erase firmware
 
 		default_do_upgrade "$1"
 		;;

target/linux/ramips/mt7621/base-files/lib/upgrade/platform.sh

@@ -31,7 +31,7 @@ platform_do_upgrade() {
 	mikrotik,routerboard-760igs|\
 	mikrotik,routerboard-m11g|\
 	mikrotik,routerboard-m33g)
-		[ -z "$(rootfs_type)" ] && mtd erase firmware
+		[ "$(rootfs_type)" = "tmpfs" ] && mtd erase firmware
 		;;
 	asus,rt-ac65p|\
 	asus,rt-ac85p)