arm64: Clear the initial ID map correctly before remapping

In the attempt to clear and recreate the initial ID map for LPA2, we
wrongly use 'start - end' as the map size and make the memset() almost a
nop.

Fix it by passing the correct map size.

Fixes: 9684ec18 ("arm64: Enable LPA2 at boot if supported by the system")
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240621092809.162-1-yuzenghui@huawei.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/pi/map_kernel.c

@@ -173,7 +173,7 @@ static void __init remap_idmap_for_lpa2(void)
 	 * Don't bother with the FDT, we no longer need it after this.
 	 */
 	memset(init_idmap_pg_dir, 0,
-	       (u64)init_idmap_pg_dir - (u64)init_idmap_pg_end);
+	       (u64)init_idmap_pg_end - (u64)init_idmap_pg_dir);
 
 	create_init_idmap(init_idmap_pg_dir, mask);
 	dsb(ishst);