tidy: Fix simple warnings of 'value stored is never read' in freesurr…

…ound.

The clang-tidy "dead stores" check pointed out several places where a
variables was set and never used.  It appears that his code used to be
part of a loop where the setting the variable would have made sense,
but now is only a single pass and the new value is never references.
Clean up these warnings by removing the assignments.

mythtv/libs/libmythfreesurround/freesurround.cpp

@@ -355,7 +355,6 @@ uint FreeSurround::receiveFrames(void *buffer, uint maxFrames)
             *output++ = *rs++;
         }
         oc -= maxFrames;
-        outindex += maxFrames;
     }
     else        // channels == 6
     {
@@ -378,7 +377,6 @@ uint FreeSurround::receiveFrames(void *buffer, uint maxFrames)
                 *output++ = *rs++;
             }
             oc -= maxFrames;
-            outindex += maxFrames;
         }
         else
         {
@@ -398,7 +396,6 @@ uint FreeSurround::receiveFrames(void *buffer, uint maxFrames)
                 *output++ = *rs++;
             }
             oc -= maxFrames;
-            outindex += maxFrames;
         }
     }
     out_count = oc;