Tweak some Max7219 code

Marlin/src/feature/Max7219_Debug_LEDs.cpp

     outbits = (outbits << 1);
     if (bits & mask)
       outbits |= 1;
-    mask = mask << 1;
+    mask <<= 1;
   }
   return outbits;
 }
       SET_PIXEL_7219((MAX7219_X_LEDS-1-x), row);
     else
       CLEAR_PIXEL_7219((MAX7219_X_LEDS-1-x), row);
-    mask = mask << 1;
+    mask <<= 1;
   }
 
   #if _ROT == 90 || _ROT == 270
       SET_PIXEL_7219(col, MAX7219_Y_LEDS-1-y);
     else
       CLEAR_PIXEL_7219(col, MAX7219_Y_LEDS-1-y);
-    mask = mask << 1;
+    mask <<= 1;
   }
   #if _ROT == 90 || _ROT == 270
     SEND_7219(col); // force the column out to the Max7219 chips and strobe them