CopyValue functions should involve volatile accesses (#720)

* CopyValue functions should involve volatile accesses

These are writing to specific registers in memory that are memory mapped to do things, so we cannot do any optimizations here regarding memory.

* match pokeemerald's style

---------

Co-authored-by: Marcus Huderle <huderlem@gmail.com>

src/scanline_effect.c

@@ -107,16 +107,16 @@ void ScanlineEffect_InitHBlankDmaTransfer(void)
 
 static void CopyValue16Bit(void)
 {
-    u16 *dest = (u16 *)gScanlineEffect.dmaDest;
-    u16 *src = (u16 *)&gScanlineEffectRegBuffers[gScanlineEffect.srcBuffer];
+    vu16 *dest = (vu16 *)gScanlineEffect.dmaDest;
+    vu16 *src = (vu16 *)&gScanlineEffectRegBuffers[gScanlineEffect.srcBuffer];
 
     *dest = *src;
 }
 
 static void CopyValue32Bit(void)
 {
-    u32 *dest = (u32 *)gScanlineEffect.dmaDest;
-    u32 *src = (u32 *)&gScanlineEffectRegBuffers[gScanlineEffect.srcBuffer];
+    vu32 *dest = (vu32 *)gScanlineEffect.dmaDest;
+    vu32 *src = (vu32 *)&gScanlineEffectRegBuffers[gScanlineEffect.srcBuffer];
 
     *dest = *src;
 }