ARM: sa1111: cleanup sub-device registration and unregistration

Move the releasing of resources out of the release function - this
allows a cleaner and more conventional arrangement of the registration
failure paths and a saner unregistration process for these devices.

Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>