piix: use DIV_ROUND_UP

I used the clang-tidy qemu-round check to generate the fix:
https://github.com/elmarco/clang-tools-extra

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>

hw/pci-host/piix.c

@@ -140,7 +140,7 @@ static void i440fx_update_memory_mappings(PCII440FXState *d)
     memory_region_transaction_begin();
     for (i = 0; i < 13; i++) {
         pam_update(&d->pam_regions[i], i,
-                   pd->config[I440FX_PAM + ((i + 1) / 2)]);
+                   pd->config[I440FX_PAM + (DIV_ROUND_UP(i, 2))]);
     }
     memory_region_set_enabled(&d->smram_region,
                               !(pd->config[I440FX_SMRAM] & SMRAM_D_OPEN));