ieee802154: mcr20a: Fix memory leak in mcr20a_probe

Free allocated memory for pdata before return.

Addresses-Coverity-ID: 1466096 ("Resource leak")
Fixes: 8c6ad9cc ("ieee802154: Add NXP MCR20A IEEE 802.15.4 transceiver driver")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Xue Liu <liuxuenetmail@gmail.com>
Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>