x86emul: correct 32-bit address handling for AVX2 gathers

As done for other cases by commit 7869e2bafe ("x86emul/fuzz: add
rudimentary limit checking"), address calculations should also use
truncate_ea() for the AVX2 gather insns.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/x86_emulate/x86_emulate.c

@@ -8400,7 +8400,8 @@ x86_emulate(
                 signed long idx = b & 1 ? index.qw[i] : index.dw[i];
 
                 rc = ops->read(ea.mem.seg,
-                               ea.mem.off + (idx << state->sib_scale),
+                               truncate_ea(ea.mem.off +
+                                           (idx << state->sib_scale)),
                                (void *)mmvalp + i * op_bytes, op_bytes, ctxt);
                 if ( rc != X86EMUL_OKAY )
                 {