Make CPURead/WriteFunc structure 'const'

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/hw/arm_timer.c b/hw/arm_timer.c
index 572804f..25cbf66 100644
--- a/hw/arm_timer.c
+++ b/hw/arm_timer.c
@@ -223,13 +223,13 @@
     }
 }
 
-static CPUReadMemoryFunc *sp804_readfn[] = {
+static CPUReadMemoryFunc * const sp804_readfn[] = {
    sp804_read,
    sp804_read,
    sp804_read
 };
 
-static CPUWriteMemoryFunc *sp804_writefn[] = {
+static CPUWriteMemoryFunc * const sp804_writefn[] = {
    sp804_write,
    sp804_write,
    sp804_write
@@ -311,13 +311,13 @@
 }
 
 
-static CPUReadMemoryFunc *icp_pit_readfn[] = {
+static CPUReadMemoryFunc * const icp_pit_readfn[] = {
    icp_pit_read,
    icp_pit_read,
    icp_pit_read
 };
 
-static CPUWriteMemoryFunc *icp_pit_writefn[] = {
+static CPUWriteMemoryFunc * const icp_pit_writefn[] = {
    icp_pit_write,
    icp_pit_write,
    icp_pit_write