drivers: ethernet: enc28j60: Prevent infinate loop on driver init

In the case that there is a situation where the controller
oscillator start-up timer doesn't expire, or the SPI can't
read the CLKRDY bit the driver would hang during init.
The config option ETH_ENC28J60_CLKRDY_INIT_WAIT_MS sets
the time that the driver will wait for OST before returning
an ETIMEDOUT error.

Signed-off-by: Dean Sellers <dsellers@evos.com.au>