kvmvapic: add ioport read accessor

Necessary since memory region accessor assumes read and write
methods are registered. Otherwise reading I/O port 0x7e segfaults.

https://bugzilla.redhat.com/show_bug.cgi?id=954306

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

hw/i386/kvmvapic.c

@@ -687,8 +687,14 @@ static void vapic_write(void *opaque, hwaddr addr, uint64_t data,
     }
 }
 
+static uint64_t vapic_read(void *opaque, hwaddr addr, unsigned size)
+{
+    return 0xffffffff;
+}
+
 static const MemoryRegionOps vapic_ops = {
     .write = vapic_write,
+    .read = vapic_read,
     .endianness = DEVICE_NATIVE_ENDIAN,
 };