tty: synclinkmp: do not ignore errors in probe()

synclinkmp_init_one() ignores all errors and does not release
all resources if something fails.

The patch adds returned code to device_init() and add_device()
and proper error handling.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>