wifi: wilc1000: get correct length of string WID from received config packet

For string type WID packet, the data length is received as 16-bit value
so use 'get_unaligned_le16' conversion API to extract the correct length.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220720160302.231516-5-ajay.kathat@microchip.com