intel_iommu: "aw-bits" error message still refers to "x-aw-bits"

Commit 4b49b586c4 ('intel_iommu: remove "x-" prefix for "aw-bits"')
removed the "x-" prefix but but didn't update the error message
accordingly.

Signed-off-by: Menno Lageman <menno.lageman@oracle.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20200625155258.1452425-1-menno.lageman@oracle.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

hw/i386/intel_iommu.c

@@ -3758,7 +3758,7 @@ static bool vtd_decide_config(IntelIOMMUState *s, Error **errp)
     /* Currently only address widths supported are 39 and 48 bits */
     if ((s->aw_bits != VTD_HOST_AW_39BIT) &&
         (s->aw_bits != VTD_HOST_AW_48BIT)) {
-        error_setg(errp, "Supported values for x-aw-bits are: %d, %d",
+        error_setg(errp, "Supported values for aw-bits are: %d, %d",
                    VTD_HOST_AW_39BIT, VTD_HOST_AW_48BIT);
         return false;
     }