enc28j60: hardware errata #14 ERXRDPT register failure

Even values in ERXRDPT register may corrupt the receive buffer.
Set ERXRDPT value one address behind the next value.
If it is zero, set the value to the reception buffer end address.

Change-Id: I7150e5190c5bfb7bfafbff598eea1c26959643d0
Signed-off-by: Juan Manuel Cruz Alcaraz <juan.m.cruz.alcaraz@intel.com>