i2c: add i2c_trylock_bus wrapper, use it

This unifies usage with i2c_lock_bus and i2c_unlock_bus, and paves the
way for the next patch which looks a bit saner with this preparatory
work taken care of beforehand.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 8eee986..764f195 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -159,7 +159,7 @@
 		return 0;	/* mux_lock not locked, failure */
 	if (!(flags & I2C_LOCK_ROOT_ADAPTER))
 		return 1;	/* we only want mux_lock, success */
-	if (parent->trylock_bus(parent, flags))
+	if (i2c_trylock_bus(parent, flags))
 		return 1;	/* parent locked too, success */
 	rt_mutex_unlock(&parent->mux_lock);
 	return 0;		/* parent not locked, failure */
@@ -193,7 +193,7 @@
 
 	if (!rt_mutex_trylock(&parent->mux_lock))
 		return 0;	/* mux_lock not locked, failure */
-	if (parent->trylock_bus(parent, flags))
+	if (i2c_trylock_bus(parent, flags))
 		return 1;	/* parent locked too, success */
 	rt_mutex_unlock(&parent->mux_lock);
 	return 0;		/* parent not locked, failure */