[PATCH] rt2x00: Allways memset memory obtained from skb_push()

When skb_push() is used we should memset the memory before
usage. This will prevent bugs which could occur when the
data is treated as TX descriptor.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>