x86/vdso: Add __user annotation to VDSO32_SYMBOL

The address calculated by VDSO32_SYMBOL() is a pointer into
userland. Add the __user annotation to fix related sparse
warnings in its users.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Andy Lutomirski <luto@MIT.EDU>
Link: http://lkml.kernel.org/r/1346621506-30857-3-git-send-email-minipli@googlemail.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>