wifi: wilc1000: validate number of channels

There is no validation of 'e->no_of_channels' which can trigger an
out-of-bounds write in the following 'memset' call. Validate that the
number of channels does not extends beyond the size of the channel list
element.

Signed-off-by: Phil Turnbull <philipturnbull@github.com>
Tested-by: Ajay Kathat <ajay.kathat@microchip.com>
Acked-by: Ajay Kathat <ajay.kathat@microchip.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221123153543.8568-5-philipturnbull@github.com