wl12xx: restore default channel configuration

wl12xx allocates two static structs wl1271_band_2ghz &
wl1271_band_5ghz which are used/modified by Reg-Domain
e.g. some channel might be marked as passive at some
point. These structs freed only during wl12xx rmmod and
aren't cleared during wl12xx_sdio.ko, this means that
some channel flags might be set regardless reg-domain
rules. Fix this by clearing the channel flags from
the previous usage (before the current wl12xx_sdio.ko
insmod).

Signed-off-by: Victor Goldenshtein <victorg@ti.com>