staging: ks7010: refactor ks_wlan_set_phy_type function

Handle invalid values first and assign good ones at the
end if it is the case. This makes code simplier.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>