firmware: minor screendump related cleanups

- Remove unused redefinitions of screen_dump() from bootloaders
- Use empty do-while when screendump is compiled out

Change-Id: I3ccdb0390ddaa28d8f561ff744d0db6aaef17f5d

bootloader/iaudio_coldfire.c

@@ -212,9 +212,3 @@ void main(void)
 
     start_firmware();
 }
-
-/* These functions are present in the firmware library, but we reimplement
-   them here because the originals do a lot more than we want */
-void screen_dump(void)
-{
-}

bootloader/iriver_h1x0.c

@@ -588,10 +588,6 @@ void main(void)
 
 /* These functions are present in the firmware library, but we reimplement
    them here because the originals do a lot more than we want */
-void screen_dump(void)
-{
-}
-
 int usb_screen(void)
 {
    return 0;

bootloader/iriver_h300.c

@@ -648,10 +648,6 @@ void main(void)
 
 /* These functions are present in the firmware library, but we reimplement
    them here because the originals do a lot more than we want */
-void screen_dump(void)
-{
-}
-
 int usb_screen(void)
 {
    return 0;

bootloader/mpio_hd200_hd300.c

@@ -539,9 +539,3 @@ void main(void)
     }
 
 }
-
-/* These functions are present in the firmware library, but we reimplement
-   them here because the originals do a lot more than we want */
-void screen_dump(void)
-{
-}

firmware/export/screendump.h

@@ -54,8 +54,8 @@
 
 #ifdef BOOTLOADER
 
-#define screen_dump()
-#define remote_screen_dump()
+#define screen_dump() do { } while(0)
+#define remote_screen_dump() do { } while(0)
 
 #else /* !BOOTLOADER */