buildroot: init: fix dev/shm and devpts fs lost in ramdisk rootfs issue.

In ramdisk case, dev/shm and devpts not mounted in ramdisk rootfs,
for the mount commands are not executed in ramdisk rootfs,
this will cause adb shell can't work.
move these commands before execute sbin/init.

Signed-off-by: minda.chen <minda.chen@starfivetech.com>

system/skeleton/init

@@ -18,10 +18,6 @@ for x in $(cat /proc/cmdline); do
 	esac
 done
 
-if [ "x${ROOT}" = "x" ]; then
-	exec /sbin/init
-fi
-
 mount -t sysfs sysfs /sys
 
 mount -t devtmpfs -o nosuid,mode=0755 devtmpfs /dev
@@ -33,6 +29,10 @@ mount -t tmpfs tmpfs /dev/shm
 mount -t tmpfs tmpfs /tmp
 mount -t tmpfs tmpfs /run
 
+if [ "x${ROOT}" = "x" ]; then
+	exec /sbin/init
+fi
+
 export ROOT
 
 mkdir /rootfs