regmap: change struct regmap's internal locks as union

this patch change struct regmap->mutex and struct regmap->spinlock
as an union, because these 2 members are only used one of them,
we change it to shrink the struct size.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/drivers/base/regmap/internal.h b/drivers/base/regmap/internal.h
index 7d13269..f82e8fa 100644
--- a/drivers/base/regmap/internal.h
+++ b/drivers/base/regmap/internal.h
@@ -49,8 +49,10 @@
 };
 
 struct regmap {
-	struct mutex mutex;
-	spinlock_t spinlock;
+	union {
+		struct mutex mutex;
+		spinlock_t spinlock;
+	};
 	unsigned long spinlock_flags;
 	regmap_lock lock;
 	regmap_unlock unlock;