x86: fix warning on 32-bit non-PAE

Fix the warning:

include2/asm/pgtable.h: In function `pte_modify':
include2/asm/pgtable.h:290: warning: left shift count >= width of type

On 32-bit PAE the virtual and physical addresses are both 32-bits,
so it ends up evaluating 1<<32.  Do the shift as a 64-bit shift then
cast to the appropriate size.  This should all be done at compile time,
and so have no effect on generated code.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Tested-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>