ACPI: battery: Convert discharge energy rate to current properly

ACPI battery interface reports its state either in mW or in mA, and
discharge rate in your case is reported in mW. power_supply interface
does not have such a parameter, so current_now parameter is used
for all cases. But in case of mW, reported discharge should
be converted into mA.

Signed-off-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Tested-by: Ferenc Wagner <wferi@niif.hu>
Signed-off-by: Len Brown <len.brown@intel.com>