ACPI: Fix ACPI battery regression introduced by commit 558073

Commit 558073dd ("ACPI: battery: Convert
discharge energy rate to current properly") caused the battery subsystem
to report wrong values of the remaining time on battery power and the
time until fully charged on Toshiba Portege R500 (and presumably on
other boxes too).

Fix the issue by correcting the conversion from mW to mA.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>