power_supply: Fix sysfs format warning

Fix format warning:

drivers/power/power_supply_sysfs.c:82: warning: format '%d' expects type 'int', but argument 4 has type 'ssize_t'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>