greybus: uart-gb: a few minor bug fixes

greybus: uart-gb: a few minor bug fixes

Here are a few small bug fixes in uart-gb.c:
    - In wait_serial_change():
        - Return -EINVAL if *none* of the relevant flags are set in
          the "arg" parameter.
        - Balance the spin_lock_irq() with an unlock call (not
          another lock).
        - Rearrange a nested if structure (not a bug fix).
    - In tty_gb_probe():
        - Reset the greybus_device driver data in case of error.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>