hostap: Use memdup_user() to reuse code

Fix coccicheck warning which recommends to
use memdup_user() instead of reimplementing its
code.

This patch fixes below coccicheck warnings:

drivers/net/wireless/intersil/hostap/hostap_ioctl.c:3044:9-16: WARNING
opportunity for memdup_user
drivers/net/wireless/intersil/hostap/hostap_ioctl.c:3806:9-16: WARNING
opportunity for memdup_user

Signed-off-by: Rajan Vaja <rajan.vaja@gmail.com>
Reviewed-by: Julian Calaby <julian.calaby@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>