[PATCH] Fix sparse warning in e100 driver.

The patch below fixes the following sparse warnings:

drivers/net/e100.c:1481:13: warning: Using plain integer as NULL pointer
drivers/net/e100.c:1767:27: warning: Using plain integer as NULL pointer
drivers/net/e100.c:1847:27: warning: Using plain integer as NULL pointer

Signed-off-by: Luiz Capitulino <lcapitulino@mandriva.com.br>
Signed-off-by: John W. Linville <linville@tuxdriver.com>