Fix malta const.
/// board specific constants
-pub const MEMORY_END: usize = 0x8a80_0000;
-pub const KERNEL_HEAP_SIZE: usize = 0x0444_0000;
+pub const MEMORY_END: usize = 0x8400_0000;
+pub const KERNEL_HEAP_SIZE: usize = 0x0200_0000;
