coding: fix doxygen docs for gsm0503_pdtch[_egprs]_decode()

Change-Id: I09a4c52f5704a6436eff524cd2ce5c35347aafde
diff --git a/src/coding/gsm0503_coding.c b/src/coding/gsm0503_coding.c
index 365ae6e..612e0ad 100644
--- a/src/coding/gsm0503_coding.c
+++ b/src/coding/gsm0503_coding.c
@@ -924,7 +924,7 @@
  *  \param usf_p unused argument ?!?
  *  \param[out] n_errors number of detected bit-errors
  *  \param[out] n_bits_total total number of decoded bits
- *  \returns 0 on success; negative on error */
+ *  \returns number of bytes decoded; negative on error */
 int gsm0503_pdtch_egprs_decode(uint8_t *l2_data, const sbit_t *bursts, uint16_t nbits,
 	uint8_t *usf_p, int *n_errors, int *n_bits_total)
 {
@@ -1013,7 +1013,7 @@
  *  \param[out] usf_p uplink stealing flag
  *  \param[out] n_errors number of detected bit-errors
  *  \param[out] n_bits_total total number of dcoded bits
- *  \returns 0 on success; negative on error */
+ *  \returns number of bytes decoded; negative on error */
 int gsm0503_pdtch_decode(uint8_t *l2_data, const sbit_t *bursts, uint8_t *usf_p,
 	int *n_errors, int *n_bits_total)
 {