iwlwifi: acpi: make iwl_get_bios_mcc() use the common acpi functions

The way iwl_get_bios_mcc() gets the WiFi package and checks for its
integrity is almost identical to the new iwl_acpi_get_wifi_pkg()
function.  Instead of having duplicate code, convert it to use the
common code.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>