arm: fix compile on bigendian host

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target-arm/cpu.h

@@ -73,7 +73,7 @@
  * significant half of a uint64_t struct member.
  */
 #ifdef HOST_WORDS_BIGENDIAN
-#define offsetoflow32(S, M) offsetof(S, M + sizeof(uint32_t))
+#define offsetoflow32(S, M) (offsetof(S, M) + sizeof(uint32_t))
 #else
 #define offsetoflow32(S, M) offsetof(S, M)
 #endif