usb: typec: tcpm: free log buf memory when remove debug file

The logbuffer memory should be freed when remove debug file.

Cc: stable@vger.kernel.org # v4.15+
Fixes: 4b4e02c8

 ("typec: tcpm: Move out of staging")
Signed-off-by: Li Jun <jun.li@nxp.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20190717080646.30421-1-jun.li@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>