module: avoid *goto*s in module_sig_check()

Let's move the common handling of the non-fatal errors after the *switch*
statement -- this avoids *goto*s inside that *switch*...

Suggested-by: Joe Perches <joe@perches.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Sergey Shtylyov <s.shtylyov@omprussia.ru>
Signed-off-by: Jessica Yu <jeyu@kernel.org>