fsa4480: Avoid updating settings if unchanged

During audio subsystem restart, the audio driver will unregister
its notifier on shutdown and re-register when subsystem is up again.
If a regular USB device, and not a Type-C analog audio device, is
currently connected, we should not re-write the register settings
over I2C to the FSA4480 IC as that will make the D+/D- pins to
be momentarily switched off an on, which causes the USB controller
to detect a momentary disconnect and re-connect of the attached
peripheral.

Fix this by first reading the switch control and enable registers,
and if being updated with the same values, don't re-write them to
avoid unnecessarily resetting D+/D- or SBU1/2.

Change-Id: I9d4e092e9782ca64caf0982958b3e5d05744aa92
Signed-off-by: Jack Pham <jackp@codeaurora.org>