[ALSA] Fix bugs with incorrectly wrapped appl_ptr

PCM Midlevel
    This patch is against alsa-driver-1.0.8.
    It covers:
        alsa-kernel/core/pcm_lib.c
    The main changes are in the first listed file.

    It corresponds to bug description:
        <https://bugtrack.alsa-project.org/alsa-bug/view.php?id=951>

    The patch does cosmetic change:

     -- Better, more universal and smaller wrapping to within
        0..runtime->boundary-1 in functions snd_pcm_lib_write1() and
        snd_pcm_lib_read1() in pcm_lib.c
Signed-off-by: Charles Levert <charles_levert@gna.org>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/core/pcm_lib.c

@@ -2141,11 +2141,9 @@ static snd_pcm_sframes_t snd_pcm_lib_write1(snd_pcm_substream_t *substream,
 			break;
 		}
 		appl_ptr += frames;
-		if (appl_ptr >= runtime->boundary) {
-			runtime->control->appl_ptr = 0;
-		} else {
-			runtime->control->appl_ptr = appl_ptr;
-		}
+		if (appl_ptr >= runtime->boundary)
+			appl_ptr -= runtime->boundary;
+		runtime->control->appl_ptr = appl_ptr;
 		if (substream->ops->ack)
 			substream->ops->ack(substream);
 
@@ -2440,11 +2438,9 @@ static snd_pcm_sframes_t snd_pcm_lib_read1(snd_pcm_substream_t *substream,
 			break;
 		}
 		appl_ptr += frames;
-		if (appl_ptr >= runtime->boundary) {
-			runtime->control->appl_ptr = 0;
-		} else {
-			runtime->control->appl_ptr = appl_ptr;
-		}
+		if (appl_ptr >= runtime->boundary)
+			appl_ptr -= runtime->boundary;
+		runtime->control->appl_ptr = appl_ptr;
 		if (substream->ops->ack)
 			substream->ops->ack(substream);