device-tolinopage2: fix post-upgrade for uboot

device/testing/u-boot-tolino-page2/u-boot-tolino-page2.post-upgrade

 #!/bin/sh
-DEV=`mount | sed -n -E 's:.*(/dev/mmcblk[0-9])p[0-9] on /boot .*:\1:p'`
-if [ -n "$DEV" ] ; then
+DEV=`cat /proc/mounts | sed -n -E 's:.*(/dev/mmcblk[0-9])p[0-9] on /boot .*:\1:p'`
+if [ -e "$DEV" ]
+then
 	dd if=/usr/share/u-boot/tolino-shine3/u-boot.imx bs=512 seek=2 of="$DEV"
+else
+    echo Partition not found
 fi