mwifiex: printk() overflow with 32-byte SSIDs

SSIDs aren't guaranteed to be 0-terminated. Let's cap the max length
when we print them out.

This can be easily noticed by connecting to a network with a 32-octet
SSID:

[ 3903.502925] mwifiex_pcie 0000:01:00.0: info: trying to associate to
'0123456789abcdef0123456789abcdef <uninitialized mem>' bssid
xx:xx:xx:xx:xx:xx

Fixes: 5e6e3a92b9a4 ("wireless: mwifiex: initial commit for Marvell mwifiex driver")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Cc: <stable@vger.kernel.org>
Acked-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>