tty: srmcons: fix retval from srmcons_init()

The value returned from srmcons_init() was -ENODEV for over 2 decades.
But it does not matter, given device_initcall() ignores retvals.

But to be honest, return 0 in case the tty driver was registered
properly.

To do that, the condition is inverted and a short path taken in case of
error.

err_free_drv is introduced as it will be used from more places later.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Tested-by: Magnus Lindholm <linmag7@gmail.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: linux-alpha@vger.kernel.org
Link: https://lore.kernel.org/r/20250317070046.24386-22-jirislaby@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>