ieee802154: adf7242: use unsigned int over only unsigned

Bring it in line with the rest of the ieee802154 drivers.
Found by checkpatch.

Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>