The get_firmware_crc() callback function isn't flexible
enough when dealing with multiple firmware versions.
It might in some cases be possible that the firmware
file contains multiple CRC checksums.

Create the check_firmware() callback function where the driver
has complete freedom in how to validate the firmware.
Signed-off-by: NIvo van Doorn <IvDoorn@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>