x86: Use correct type for %cr4

%cr4 is 64-bit in 64-bit mode (although the upper 32-bits are currently reserved).
Use unsigned long for the temporary variable to get the right size.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <1283563039-3466-2-git-send-email-brgerst@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>