Update 'gXcp.MtaPtr' in XcpReadMta() and XcpWriteMta(). (#47)

Bug was introduced in V5.4 with commit 832e0da.
In case of multiple consecutive CC_UPLOAD requests from CANape, XcpReadMta() has to update 'gXcp.MtaPtr'.
An example sequence sent by CANape would be: CC_SET_MTA -> CC_UPLOAD -> CC_UPLOAD.
In case of multiple consecutive CC_DOWNLOAD requests from CANape, XcpWriteMta() has to update 'gXcp.MtaPtr'.
An example sequence sent by CANape would be: CC_SET_MTA -> CC_DOWNLOAD -> CC_DOWNLOAD.
Also corrected comment above XcpReadMta().

src/xcpLite.c

@@ -372,13 +372,14 @@ static uint8_t XcpWriteMta( uint8_t size, const uint8_t* data )
     if (gXcp.MtaExt == 0x00) {
         if (gXcp.MtaPtr == NULL) return CRC_ACCESS_DENIED;
         memcpy(gXcp.MtaPtr, data, size);
+        gXcp.MtaPtr += size;
         return 0; // Ok
     }
 
     return CRC_ACCESS_DENIED; // Access violation
 }
 
-// Read n bytes. Copying of size bytes from data to gXcp.MtaPtr
+// Read n bytes. Copying of size bytes from gXcp.MtaPtr to data
 static uint8_t XcpReadMta( uint8_t size, uint8_t* data )
 {
     // Ext=0x01 Relativ addressing
@@ -401,6 +402,7 @@ static uint8_t XcpReadMta( uint8_t size, uint8_t* data )
     if (gXcp.MtaExt == 0x00) {
         if (gXcp.MtaPtr == NULL) return CRC_ACCESS_DENIED;
         memcpy(data, gXcp.MtaPtr, size);
+        gXcp.MtaPtr += size;
         return 0; // Ok
     }