[ALSA] Fix the OSS PCM emulation - O_NONBLOCK write

ALSA<-OSS emulation
This patch fixes the OSS PCM write() in O_NONBLOCK mode.
The previous code had not returned partial written bytes.
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/core/oss/pcm_oss.c

@@ -834,9 +834,14 @@ static ssize_t snd_pcm_oss_write1(snd_pcm_substream_t *substream, const char __u
 				if (tmp <= 0)
 					return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
 				runtime->oss.bytes += tmp;
-				runtime->oss.buffer_used = 0;
 				runtime->oss.period_ptr += tmp;
 				runtime->oss.period_ptr %= runtime->oss.period_bytes;
+				if ((substream->ffile->f_flags & O_NONBLOCK) != 0 &&
+				    tmp != runtime->oss.buffer_used) {
+					runtime->oss.buffer_used = 0;
+					break;
+				}
+				runtime->oss.buffer_used = 0;
 			}
 		} else {
 			tmp = snd_pcm_oss_write2(substream, (char *)buf, runtime->oss.period_bytes, 0);
@@ -846,6 +851,9 @@ static ssize_t snd_pcm_oss_write1(snd_pcm_substream_t *substream, const char __u
 			buf += tmp;
 			bytes -= tmp;
 			xfer += tmp;
+			if ((substream->ffile->f_flags & O_NONBLOCK) != 0 &&
+			    tmp != runtime->oss.period_bytes)
+				break;
 		}
 	}
 	return xfer;