dynamic_debug: change __dynamic_<foo>_dbg return types to void

The return value is not used by callers of these functions
so change the functions to return void.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>