Use labels instead of constants for HRAM

Use explicit ldh instruction to access HRAM locations, don't rely on optimizing ld

engine/battle/read_trainer_party.asm

@@ -315,9 +315,9 @@ ComputeTrainerReward:
 	ld hl, wBattleReward
 	xor a
 	ld [hli], a
-	ld a, [hProduct + 2]
+	ldh a, [hProduct + 2]
 	ld [hli], a
-	ld a, [hProduct + 3]
+	ldh a, [hProduct + 3]
 	ld [hl], a
 	ret