staging: ks7010: replace KS_WLAN_DEBUG with DEBUG preprocessor directive

This commit replaces custom KS_WLAN_DEBUG which is not being used anymore
in favour of DEBUG which is the one included when debugging is enabled.

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