rsi: advertise 5GHz support based on device capability

Currently 5GHz gets advertised even for the device which supports
only 2.4Ghz band. This patch fixes the issue

Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Siva Rebbagondla <siva.rebbagondla@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>