power: supply: Fix power_supply_am_i_supplied to return -ENODEV when apropriate

Commit 2848e039 ("power: supply: Make power_supply_am_i_supplied return
-ENODEV if there are no suppliers") was supposed to make
power_supply_am_i_supplied() return -ENODEV when there are no supplies
which supply the supply passed to it.

But instead it will only return -ENODEV when there are no supplies at
all as data->count++; is incremented on every call of the iterator, rather
then only when __power_supply_is_supplied_by returns true. This commit
fixes this.

Fixes: 2848e039 ("power: supply: Make power_supply_am_i_supplied ...")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>