iio: accel: mma9553: return 0 as indication of success

Use return 0 instead of return ret to mark
clearly the success return path.

Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Suggested-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>