Change usb_printing_counter to uint8_t

It is assigned max value of 10

Saves 26 byte of flash and 1 byte of SRAM

Firmware/Marlin.h

@@ -319,7 +319,7 @@ extern int bowden_length[4];
 extern bool is_usb_printing;
 extern bool homing_flag;
 extern bool loading_flag;
-extern unsigned int usb_printing_counter;
+extern uint8_t usb_printing_counter;
 extern unsigned long total_filament_used;
 void save_statistics(unsigned long _total_filament_used, unsigned long _total_print_time);
 extern unsigned int heating_status;

Firmware/Marlin_main.cpp

@@ -195,7 +195,7 @@ int bowden_length[4] = {385, 385, 385, 385};
 bool is_usb_printing = false;
 bool homing_flag = false;
 
-unsigned int  usb_printing_counter;
+uint8_t usb_printing_counter;
 
 int8_t lcd_change_fil_state = 0;