avcodec/ivi: make comments more Doxygen-friendly

Doxygen eats the newline in the first comment, making it harder to read.
Join the lines and add a comma, so source and documentation are equally readable.

Doxygen only associates the second comment with cust_dec.
The comments for cust_dec and cust_tab make perfect sense without it,
so downgrade it to a non-doxygen "//" comment.

The third comment was missed by the command in the previous commit,
because it (correctly but uniquely) doesn't have a trailing comma.
Signed-off-by: Andrew Sayers <ffmpeg-devel@pileofstuff.org>

libavcodec/ivi.h

@@ -61,18 +61,17 @@ typedef struct IVIHuffDesc {
  *  macroblock/block huffman table descriptor
  */
 typedef struct IVIHuffTab {
-    int32_t     tab_sel;    ///< index of one of the predefined tables
-                            /// or "7" for custom one
+    int32_t     tab_sel;    ///< index of one of the predefined tables, or "7" for custom one
     VLC         *tab;       ///< pointer to the table associated with tab_sel
 
-    /// the following are used only when tab_sel == 7
+    // the following are used only when tab_sel == 7
     IVIHuffDesc cust_desc;  ///< custom Huffman codebook descriptor
     VLC         cust_tab;   ///< vlc table for custom codebook
 } IVIHuffTab;
 
 enum {
     IVI_MB_HUFF   = 0,      ///< Huffman table is used for coding macroblocks
-    IVI_BLK_HUFF  = 1       /// Huffman table is used for coding blocks
+    IVI_BLK_HUFF  = 1       ///< Huffman table is used for coding blocks
 };