[ALSA] sound/synth/util_mem.c: remove pointless check

The Coverity checker spotted that if anyone would call this function
with 'prev == NULL', he would still get an Oops a few lines below.
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/synth/util_mem.c

@@ -116,7 +116,7 @@ __snd_util_memblk_new(struct snd_util_memhdr *hdr, unsigned int units,
 	if (blk == NULL)
 		return NULL;
 
-	if (! prev || prev == &hdr->block)
+	if (prev == &hdr->block)
 		blk->offset = 0;
 	else {
 		struct snd_util_memblk *p = get_memblk(prev);