dynamic_printk: reduce one level of indentation

Cleanup pr_debug_write() to reduce one level of indentation.

Cc: Marcel Holtmann <marcel@holtmann.org>
Acked-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>