dynamic_debug: drop explicit !=NULL checks

Convert 'if (x !=NULL)' checks into 'if (x)'.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>