🩹 Fix memset block warning

Marlin/src/module/planner.cpp

   block_t * const block = get_next_free_block(next_buffer_head);
 
   // Clear block
-  memset(block, 0, sizeof(block_t));
+  block->reset();
 
   block->flag.apply(sync_flag);
 

Marlin/src/module/planner.h

     block_laser_t laser;
   #endif
 
+  void reset() { memset((char*)this, 0, sizeof(*this)); }
+
 } block_t;
 
 #if ANY(LIN_ADVANCE, SCARA_FEEDRATE_SCALING, GRADIENT_MIX, LCD_SHOW_E_TOTAL, POWER_LOSS_RECOVERY)