staging: ks7010: refactor hostif_sme_power_mgmt_set function

This commit refactor hostif_sme_power_mgmt_set avoiding to
use switch-case statement and simplifying data paths. This
improves readability.

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