can: softing: softing_startstop(): fix set but not used variable warning

can: softing: softing_startstop(): fix set but not used variable warning

In the function softing_startstop() the variable error_reporting is
assigned but not used. The code that uses this variable is commented
out. Its stated that the functionality is not finally verified.

To fix the warning:

| drivers/net/can/softing/softing_fw.c:424:9: error: variable 'error_reporting' set but not used [-Werror,-Wunused-but-set-variable]

remove the comment, activate the code, but add a "0 &&" to the if
expression and rely on the optimizer rather than the preprocessor to
remove the code.

Link: https://lore.kernel.org/all/20220109103126.1872833-1-mkl@pengutronix.de
Fixes: 03fd3cf5a179 ("can: add driver for Softing card")
Cc: Kurt Van Dijck <dev.kurt@vandijck-laurijssen.be>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>