fix deprecated volatile compound assignment (#152)

* fixed deprecated volatile compound assignment

C++20 deprecates some undefined or unclear use cases of 'volatile' like
compound assignments and compliant compilers warn about those deprecated
operations.

In vStreamBufferMoveMid the deprecated compound assignment and other
direct accesses to volatile 'StreamBuffer_t->uxMid' is replaced using a
local variable stored back when done.

* Uncrustify

Co-authored-by: Aniruddha Kanhere <[email protected]>
Co-authored-by: Aniruddha Kanhere <[email protected]>

Author: hs2gh

include/FreeRTOS_Stream_Buffer.h

@@ -163,19 +163,22 @@
     {
 /* Increment uxMid, but no further than uxHead */
         size_t uxSize = uxStreamBufferMidSpace( pxBuffer );
+        size_t uxMid = pxBuffer->uxMid;
         size_t uxMoveCount = uxCount;
 
         if( uxMoveCount > uxSize )
         {
             uxMoveCount = uxSize;
         }
 
-        pxBuffer->uxMid += uxMoveCount;
+        uxMid += uxMoveCount;
 
-        if( pxBuffer->uxMid >= pxBuffer->LENGTH )
+        if( uxMid >= pxBuffer->LENGTH )
         {
-            pxBuffer->uxMid -= pxBuffer->LENGTH;
+            uxMid -= pxBuffer->LENGTH;
         }
+
+        pxBuffer->uxMid = uxMid;
     }
 /*-----------------------------------------------------------*/