staging: rtl8192u: ieee80211: Remove redundant memset

alloc_etherdev function internally calls kvzalloc . So we may not need
explicit memset after this call.

Signed-off-by: Hariprasad Kelam <hariprasad.kelam@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>