Fix small font section directive, mixer warning

Marlin/src/lcd/dogm/fontdata/fontdata_6x9_marlin.h

   Max Font    ascent = 7 descent=-2
 */
 #include <U8glib.h>
-const u8g_fntpgm_uint8_t u8g_font_6x9[2300] U8G_SECTION(".progmem.u8g_font_6x9") = {
+const u8g_fntpgm_uint8_t u8g_font_6x9[2300] U8G_FONT_SECTION(".progmem.u8g_font_6x9") = {
   0, 6, 9, 0, 254, 6, 1, 137, 2, 254, 32, 255, 254, 7, 254, 6,
   254, 0, 0, 0, 6, 0, 7, 1, 6, 6, 6, 2, 0, 128, 128, 128,
   128, 0, 128, 3, 3, 3, 6, 1, 3, 160, 160, 160, 5, 7, 7, 6,

Marlin/src/lcd/dogm/status_screen_DOGM.cpp

 
         // Two-component mix / gradient instead of XY
 
-        char mixer_messages[12];
+        char mixer_messages[15];
         PGM_P mix_label;
         #if ENABLED(GRADIENT_MIX)
           if (mixer.gradient.enabled) {