Fix mbtk gnss.

Change-Id: I08476f2f51cd7b0f7898b109201302409d76a6d2
diff --git a/mbtk/libmbtk_gnss/mbtk_gnss.c b/mbtk/libmbtk_gnss/mbtk_gnss.c
index 515feae..11bbfd3 100755
--- a/mbtk/libmbtk_gnss/mbtk_gnss.c
+++ b/mbtk/libmbtk_gnss/mbtk_gnss.c
@@ -353,6 +353,24 @@
     return GNSS_ERR_OK;
 }
 
+/*===========================================================================
+FUNCTION mbtk_gnss_open
+
+DESCRIPTION:
+  Open/Close GNSS.
+
+PARAMETERS:
+  type [IN]: How to turn on or off GNSS,The available values are as follows:
+           0 : Close GNSS;
+           1-15 : Open GNSS with NMEA print;
+              (GNSS_PRINT_PORT_UART1 / GNSS_PRINT_PORT_USB_NMEA / GNSS_PRINT_PORT_USB_AT / GNSS_PRINT_PORT_TTY_AT)
+           Other : Open GNSS without print NMEA
+  timeout [IN]: Timeout with second.
+
+RETURN VALUE:
+  gnss_err_enum
+
+===========================================================================*/
 gnss_err_enum mbtk_gnss_open(int type, int timeout)
 {
     if(gnss_cli_fd < 0) {
@@ -481,7 +499,13 @@
     }
 }
 
-
+/**
+* Set GNSS data callback.
+*
+* gnss_ind : MBTK_GNSS_IND_LOCATION / MBTK_GNSS_IND_NMEA
+* timeout : Timeout with second.
+*
+*/
 gnss_err_enum mbtk_gnss_ind_set(uint32 gnss_ind, int timeout)
 {
     if(gnss_cli_fd < 0) {