drm/i915/gvt: fix bad 32 bit shift in gtt

Since ioread32 returns a 32-bit value, it is impossible to left-shift
this value by 32 bits (it produces a compilation error). Casting the
return value of ioread32 fix this issue.
Signed-off-by: Jérémy Lefaure <jeremy.lefaure@lse.epita.fr>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/gtt.c

@@ -276,7 +276,7 @@ static u64 read_pte64(struct drm_i915_private *dev_priv, unsigned long index)
 	pte = readq(addr);
 #else
 	pte = ioread32(addr);
-	pte |= ioread32(addr + 4) << 32;
+	pte |= (u64)ioread32(addr + 4) << 32;
 #endif
 	return pte;
 }