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>
diff --git a/arch/x86/include/asm/posix_types.h b/arch/x86/include/asm/posix_types.h
index dbcea7f..e1ed9bc 100644
--- a/arch/x86/include/asm/posix_types.h
+++ b/arch/x86/include/asm/posix_types.h
@@ -20,11 +20,12 @@
 #if defined(__x86_64__)
 typedef unsigned long	__kernel_size_t;
 typedef long		__kernel_ssize_t;
+typedef long		__kernel_ptrdiff_t;
 #else
 typedef unsigned int	__kernel_size_t;
 typedef int		__kernel_ssize_t;
-#endif
 typedef int		__kernel_ptrdiff_t;
+#endif
 typedef long		__kernel_time_t;
 typedef long		__kernel_suseconds_t;
 typedef long		__kernel_clock_t;