wifi: wilc1000: validate length of IEEE80211_P2P_ATTR_OPER_CHANNEL attribute

Validate that the IEEE80211_P2P_ATTR_OPER_CHANNEL attribute contains
enough space for a 'struct struct wilc_attr_oper_ch'. If the attribute is
too small then it triggers an out-of-bounds write later in the function.

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/20221123153543.8568-3-philipturnbull@github.com