avdevice/oss_dec: account for sample size when computing timestamp

Don't assume each sample is one byte in size. Doing so results in wrong and
occasionally non-monotonically-increasing timestamps.

Fix nearby cosmetic typo.

Signed-off-by: Marton Balint <cus@passwd.hu>

libavdevice/oss.h

@@ -30,6 +30,7 @@ typedef struct OSSAudioData {
     AVClass *class;
     int fd;
     int sample_rate;
+    int sample_size; /* in bytes ! */
     int channels;
     int frame_size; /* in bytes ! */
     enum AVCodecID codec_id;