staging: wilc1000: fix coding style of kmalloc usage

This patch fixes coding style of kmalloc usage found by checkpatch.
CHECK: Prefer kmalloc(sizeof(*new_msg)...) over kmalloc(sizeof(struct message)...)

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