acpi_extract: fix off-by-one

Single-byte package length values do use bits 4-5, and this will
happen with the PCI hotplug devices.  pkglenbytes has not yet been
decremented, so multi-byte values are detected with pkglenbytes > 1.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/tools/acpi_extract.py b/tools/acpi_extract.py
index 167a322..81fa4aa 100755
--- a/tools/acpi_extract.py
+++ b/tools/acpi_extract.py
@@ -93,7 +93,7 @@
     pkglenbytes = aml_pkglen_bytes(offset)
     pkglen = aml[offset] & 0x3F
     # If multibyte, first nibble only uses bits 0-3
-    if ((pkglenbytes > 0) and (pkglen & 0x30)):
+    if ((pkglenbytes > 1) and (pkglen & 0x30)):
         die("PkgLen bytes 0x%x but first nibble 0x%x expected 0x0X" %
             (pkglen, pkglen))
     offset += 1