x86: Fix ptrdiff_t for x86_64

sbrk() assumes ptrdiff_t is large enough to enlarge/shrink the heap
by LONG_MIN/LONG_MAX.
So, use the long type, also to match the rest of the Linux ecosystem.

Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Simon Glass <sjg@chromium.org>
1 file changed