staging: ks7010: refactor ks_wlan_set_cts_mode function

This commit refactors ks_wlan_set_cts_mode function to
handle invalid values first and then assign the good
one changing a bit logic to use a ternary operator.

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