Fix Kobo startup script w/ KSM

pkill probably only checks the actual name of the binary.
We were checking a shell script, which I'm guessing is not launched
via a shebang, so that name was actually an arg to sh, or something like
that.

Use pidof instead, which matches the full command line.

platform/kobo/koreader.sh

@@ -89,7 +89,7 @@ else
 	# if we were called from advboot then we must reboot to go to the menu
 	# NOTE: This is actually achieved by checking if KSM is running:
 	#       This might lead to false-positives if you use neither KSM nor advboot to launch KOReader *without nickel running*.
-	if ! pkill -0 ksmhome.sh ; then
+	if ! pidof ksmhome.sh > /dev/null 2>&1 ; then
 		reboot
 	fi
 fi