When a client connects in HT mode but does not provide any valid MCS
rates, the function that finds the next sample rate gets stuck in an
infinite loop.
Fix this by falling back to legacy rates if no usable MCS rates are found.
Signed-off-by: NFelix Fietkau <nbd@openwrt.org>
Cc: stable@kernel.org
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>