net: ena: remove superfluous check in ena_remove()

The check in ena_remove() for the pci driver data not being NULL is not
needed, since it is always set in the probe() function. Remove the
superfluous check.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>