staging: wilc1000: linux_wlan_spi.c: fix kzalloc error check

This patch fixes error check of kzalloc.
If kzalloc is failed, return type is used as -ENOMEM.

Signed-off-by: Chaehyun Lim <chaehyun.lim@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>