[PATCH] I2C: Fix sgi_xfer return value

The sgi_xfer function returns 0 on success instead of the number of
transfered messages as it is supposed to. This patch fixes that.

Let's just hope that no client chip driver was relying on this
misbehavior.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>