ACPI: EC: Avoid returning AE_OK on errors in address space handler

If an error code other than EINVAL, ENODEV or ETIME is returned
by acpi_ec_read() / acpi_ec_write(), then AE_OK is incorrectly
returned by acpi_ec_space_handler().

Fix this by only returning AE_OK on success, and return AE_ERROR
otherwise.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>