staging: rtl8723au: rtl8723a_cmd.c: Properly initialize seq_ctrl

Control frames will not be fragmented, so we should fully initialize
the seq_ctrl field to zero. This avoids leftover stack bits remaining
set in the generated frame's seq_ctrl field.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>