drivers/atm/eni.h: remove unused macro KERNEL_OFFSET

KERNEL_OFFSET macro in eni.h is not required as it is not used anywhere. 
Remove the unused macro from eni.h header file.

Signed-off-by: Pradeep Singh <rautelap@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>