Fix compiler warnings: sketch/Marlin_main.cpp:923:19: warning: missing initializer for member '__file::unget' [-Wmissing-field-initializers]

 FILE _uartout = {0};
sketch/Marlin_main.cpp:923:19: warning: missing initializer for member '__file::flags' [-Wmissing-field-initializers]
sketch/Marlin_main.cpp:923:19: warning: missing initializer for member '__file::size' [-Wmissing-field-initializers]
sketch/Marlin_main.cpp:923:19: warning: missing initializer for member '__file::len' [-Wmissing-field-initializers]
sketch/Marlin_main.cpp:923:19: warning: missing initializer for member '__file::put' [-Wmissing-field-initializers]
sketch/Marlin_main.cpp:923:19: warning: missing initializer for member '__file::get' [-Wmissing-field-initializers]
sketch/Marlin_main.cpp:923:19: warning: missing initializer for member '__file::udata' [-Wmissing-field-initializers]

Firmware/Marlin_main.cpp

@@ -920,7 +920,7 @@ if((eSoundMode==e_SOUND_MODE_LOUD)||(eSoundMode==e_SOUND_MODE_ONCE))
 }
 
 
-FILE _uartout = {0};
+FILE _uartout; //= {0}; Global variable is always zero initialized. No need to explicitly state this.
 
 int uart_putchar(char c, FILE *stream)
 {