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 <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/include/asm/vdso.h

···
 #define VDSO32_SYMBOL(base, name)					\
 ({									\
 	extern const char VDSO32_##name[];				\
-	(void *)(VDSO32_##name - VDSO32_PRELINK + (unsigned long)(base)); \
+	(void __user *)(VDSO32_##name - VDSO32_PRELINK +		\
+			(unsigned long)(base));				\
 })
 #endif