lpm: fix charging mode sysfs param location

should be /sys/module/kernel/parameters/lpm_boot but doesnt works

else, /sys/class/power_supply/battery/batt_charging_source is set to "2"
when a branded charger is connected ("1" on normal USB to PC cable)

Change-Id: Id61ae9b03b4313f7e312a3a84db88cd9df664cce
Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>