target-i386: fix decoding of negative 4-byte displacements

Negative four byte displacements need to be sign-extended after
c086b783eb7a578993d6d2ab62c4c2666800b63d.  Do so.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Richard Henderson  <rth@twiddle.net>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

target-i386/translate.c

diff --git a/target-i386/translate.c b/target-i386/translate.c
index 38c6016..708b0a1 100644
--- a/target-i386/translate.c
+++ b/target-i386/translate.c
@@ -2016,7 +2016,7 @@
             break;
         default:
         case 2:
-            disp = ldl_code(s->pc);
+            disp = (int32_t)ldl_code(s->pc);
             s->pc += 4;
             break;
         }