net: wireless: bcmdhd: Ensure chbuckets dont overwrite

Gscan: If total number of channels from all chbuckets > 64 there is
a chance that we may overshoot when filling in channel bucket information
for FW because of differing chbucket counts between what dhd has and what
can be programmed to FW.

BUG=24469238

Signed-off-by: Ashwin <ashwin.bhat@broadcom.com>