ALSA: fireworks: Use safer way to arrange ring buffer pointer

To reverse a pointer for the ring buffer, subtraction by buffer
size is better than assignment to the beginning of the buffer.
Signed-off-by: NTakashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/firewire/fireworks/fireworks_hwdep.c

@@ -58,7 +58,7 @@ hwdep_read_resp_buf(struct snd_efw *efw, char __user *buf, long remained,
 			efw->pull_ptr += till_end;
 			if (efw->pull_ptr >= efw->resp_buf +
 					     snd_efw_resp_buf_size)
-				efw->pull_ptr = efw->resp_buf;
+				efw->pull_ptr -= snd_efw_resp_buf_size;
 
 			length -= till_end;
 			buf += till_end;

sound/firewire/fireworks/fireworks_transaction.c

@@ -148,7 +148,7 @@ copy_resp_to_buf(struct snd_efw *efw, void *data, size_t length, int *rcode)
 
 		efw->push_ptr += till_end;
 		if (efw->push_ptr >= efw->resp_buf + snd_efw_resp_buf_size)
-			efw->push_ptr = efw->resp_buf;
+			efw->push_ptr -= snd_efw_resp_buf_size;
 
 		length -= till_end;
 		data += till_end;