x86/platform_hypercall: address violations of MISRA C:2012 Rule 11.8

Add const qualifier in cast that unnecessarily removes it
to comply with Rule 11.8.
The variable info is declared with a const qualified type.
No functional change.

Signed-off-by: Maria Celeste Cesario  <maria.celeste.cesario@bugseng.com>
Signed-off-by: Simone Ballarin  <simone.ballarin@bugseng.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/platform_hypercall.c

@@ -364,7 +364,7 @@ ret_t do_platform_op(
             if ( length > info->edd_device_params.length )
                 length = info->edd_device_params.length;
             if ( copy_to_compat(op->u.firmware_info.u.disk_info.edd_params,
-                                (u8 *)&info->edd_device_params,
+                                (const uint8_t *)&info->edd_device_params,
                                 length) )
                 break;
             if ( copy_to_compat(op->u.firmware_info.u.disk_info.edd_params,