staging: r8712u: cleanup pointer type in r8712_setassocsta_cmd()

This seems like a cut and paste bug.  Smatch complains that we don't
allocate enough memory for a set_stakey_rsp struct.  In fact this is
used as a set_assocsta_rsp struct throughout and that also matches the
name of the function.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>