There is no ENC28J60_WRITEVERIFY, instead the Kconfig file defines
DRIVER_NET_ENC28J60_WRITEVERIFY. This has been this way since the very
first commit adding the driver.

The option is off by default, so this shouldn't break anything that
didn't mess with the option. Fix the typo.

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>