USB rio500.c: fix check-after-use

The Coverity checker spotted that we have already oops'ed if "dev"
was NULL in these places.

Since "dev" being NULL isn't possible at these places this patch removes
the NULL checks.

Additionally, I've fixed the formatting of the if's.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>