net: encx24j600: Fix SPI id table definition

A driver's SPI id table is expected to be an array of struct spi_device_id
that ends with a zero-initialized sentinel entry. But this driver defines
the table as a single struct spi_device_id and sets .id_table to a pointer
to this struct.

But spi_match_id() has a loop that iterates while the struct spi_device_id
.name[0] is not NULL, so not having a sentinel can cause a NULL pointer
deference error.

This patch defines the SPI id table correctly as all other SPI drivers do.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>