Instead of passing FatFS structs around, unmount; other changes

fusee/fusee-secondary/src/splash_screen_default.c

@@ -1,3 +1,3 @@
 #include "splash_screen.h"
 
-unsigned char g_default_splash_screen[1] = {0};
+uint8_t g_default_splash_screen[1] = {0};