spi: Micrel eth switch: declare missing of table

Add missing <of_device_id> table for SPI driver relying on SPI
device match since compatible is in a DT binding or in a DTS.

Before this patch:
modinfo drivers/net/phy/spi_ks8995.ko | grep alias
alias:          spi:ksz8795
alias:          spi:ksz8864
alias:          spi:ks8995

After this patch:
modinfo drivers/net/phy/spi_ks8995.ko | grep alias
alias:          spi:ksz8795
alias:          spi:ksz8864
alias:          spi:ks8995
alias:          of:N*T*Cmicrel,ksz8795C*
alias:          of:N*T*Cmicrel,ksz8795
alias:          of:N*T*Cmicrel,ksz8864C*
alias:          of:N*T*Cmicrel,ksz8864
alias:          of:N*T*Cmicrel,ks8995C*
alias:          of:N*T*Cmicrel,ks8995

Reported-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Daniel Gomez <dagmcr@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>