drivers: wifi: siwx91x: Disable HT capabilities on channel 14

In the Japan regulatory domain, channel 14 is restricted to
802.11b/g operation and does not support HT (802.11n) capabilities.
Disable HT capabilities when operating on channel 14 in AP mode.

Signed-off-by: Arunmani Alagarsamy <arunmani.a@silabs.com>