x86, gcc-4.6: Avoid unused by set variables in rdmsr

Avoids quite a lot of warnings with a gcc 4.6 -Wall build
because this happens in a commonly used header file (apic.h)

Signed-off-by: Andi Kleen <ak@linux.intel.com>
LKML-Reference: <201007202219.o6KMJme6021066@imap1.linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/msr.h

@@ -148,8 +148,8 @@ static inline unsigned long long native_read_pmc(int counter)
 #define rdmsr(msr, val1, val2)					\
 do {								\
 	u64 __val = native_read_msr((msr));			\
-	(val1) = (u32)__val;					\
-	(val2) = (u32)(__val >> 32);				\
+	(void)((val1) = (u32)__val);				\
+	(void)((val2) = (u32)(__val >> 32));			\
 } while (0)
 
 static inline void wrmsr(unsigned msr, unsigned low, unsigned high)