usb: typec: tcpm: Ignore unsupported/unknown alternate mode requests

usb: typec: tcpm: Ignore unsupported/unknown alternate mode requests

TCPM may receive PD messages associated with unknown or unsupported
alternate modes. If that happens, calls to typec_match_altmode()
will return NULL. The tcpm code does not currently take this into
account. This results in crashes.

Unable to handle kernel NULL pointer dereference at virtual address 000001f0
pgd = 41dad9a1
[000001f0] *pgd=00000000
Internal error: Oops: 5 [#1] THUMB2
Modules linked in: tcpci tcpm
CPU: 0 PID: 2338 Comm: kworker/u2:0 Not tainted 5.1.18-sama5-armv7-r2 #6
Hardware name: Atmel SAMA5
Workqueue: 2-0050 tcpm_pd_rx_handler [tcpm]
PC is at typec_altmode_attention+0x0/0x14
LR is at tcpm_pd_rx_handler+0xa3b/0xda0 [tcpm]
...
[<c03fbee8>] (typec_altmode_attention) from [<bf8030fb>]
				(tcpm_pd_rx_handler+0xa3b/0xda0 [tcpm])
[<bf8030fb>] (tcpm_pd_rx_handler [tcpm]) from [<c012082b>]
				(process_one_work+0x123/0x2a8)
[<c012082b>] (process_one_work) from [<c0120a6d>]
				(worker_thread+0xbd/0x3b0)
[<c0120a6d>] (worker_thread) from [<c012431f>] (kthread+0xcf/0xf4)
[<c012431f>] (kthread) from [<c01010f9>] (ret_from_fork+0x11/0x38)

Ignore PD messages if the associated alternate mode is not supported.

Fixes: e9576fe8e605c ("usb: typec: tcpm: Support for Alternate Modes")
Cc: stable <stable@vger.kernel.org>
Reported-by: Douglas Gilbert <dgilbert@interlog.com>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Tested-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1564761822-13984-1-git-send-email-linux@roeck-us.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>