Make CPURead/WriteFunc structure 'const'

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/hw/fdc.c b/hw/fdc.c
index c55560f..dabbf3a 100644
--- a/hw/fdc.c
+++ b/hw/fdc.c
@@ -603,25 +603,25 @@
     fdctrl_write(opaque, (uint32_t)reg, value);
 }
 
-static CPUReadMemoryFunc *fdctrl_mem_read[3] = {
+static CPUReadMemoryFunc * const fdctrl_mem_read[3] = {
     fdctrl_read_mem,
     fdctrl_read_mem,
     fdctrl_read_mem,
 };
 
-static CPUWriteMemoryFunc *fdctrl_mem_write[3] = {
+static CPUWriteMemoryFunc * const fdctrl_mem_write[3] = {
     fdctrl_write_mem,
     fdctrl_write_mem,
     fdctrl_write_mem,
 };
 
-static CPUReadMemoryFunc *fdctrl_mem_read_strict[3] = {
+static CPUReadMemoryFunc * const fdctrl_mem_read_strict[3] = {
     fdctrl_read_mem,
     NULL,
     NULL,
 };
 
-static CPUWriteMemoryFunc *fdctrl_mem_write_strict[3] = {
+static CPUWriteMemoryFunc * const fdctrl_mem_write_strict[3] = {
     fdctrl_write_mem,
     NULL,
     NULL,