sound: Re-arrange a calculation in dsp_mmap_single()

This makes it easier to read. No functional change intended.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Reviewed by:	markj, kib
Pull-Request:	https://ron-dev.freebsd.org/FreeBSD/src/pulls/30

sys/dev/sound/pcm/dsp.c

@@ -1993,7 +1993,7 @@ dsp_mmap_single(struct cdev *cdev, vm_ooffset_t *offset,
 
 	CHN_LOCK(c);
 	if ((c->flags & CHN_F_MMAP_INVALID) ||
-	    *offset + size > c->bufsoft->allocsize) {
+	    c->bufsoft->allocsize < *offset + size) {
 		CHN_UNLOCK(c);
 		PCM_GIANT_EXIT(d);
 		return (EINVAL);