ep93xx: some minor cleanups to the ep93xx eth driver

Small cleanup in the Cirrus Logic EP93xx ethernet driver: Check for NULL
pointer before dereferencing it instead of after.  Remove unreferenced
variable.

Signed-off-by: Yan Burman <burman.yan@gmail.com>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>