mwifiex: use maximum ssid length as 0xfe for p2p

0xfe is basically a magic number used to ask firmware match
provided string in a SSID. In this case, firmware will
return scan results containing"DIRECT-" string.

Signed-off-by: Aniket Nagarnaik <aniketn@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>