There is already a bus driver for omap4460 in the Linux kernel. You can look at the kernel messages to see if this driver is being enabled during boot. If your interest is just accessing the device, you can do that from user-space without having to write a client driver. There is a good tutorial here. But if you are writing a driver as an exercise or you need access to other kernel features in the driver, then you can look at any driver in the drivers/rtc directory of the kernel, there are loads of good examples there.
Just found iio driver for hmc5843 in drivers/staging/iio/magnetometer which is very similar to what you want, it might work straight away without any modifications if you are lucky.