At connection time (or boot) in si2168_probe(), the firmware is not
loaded to the device and the device is not fully activated. It is
not useful or sensible to do this full initialization on resume in
case it has not been previously initialized and is expected to be
in this initialized state.
Calling si2168_init() and therefore reading the firmware file for
the first time during resume leads to problems and should be avoided.
It is however safe to read the firmware file once it has already been
read outside of a suspend/resume situation.

Add a staus flag 'initialized' to store whether si2168_init() has
successfully been called. If initialization fails (e.g. due to missing
firmware file), the flag is not set.
Register a separate si2168_resume callback which only calls
si2168_init() once the 'initialized' flag has been set and it is safe
to load the firmware at resume.
The first call to si2168_init() will now always happen when the device
is actually used for the first time and never during resume.
This avoids the unsafe firmware file reading and should also speed up
resume by skipping unnecessary device initialization.

Link: https://lore.kernel.org/linux-media/20210418001204.7453-3-kernel@tuxforce.de

[mchehab: fix several Coding Style issues]
Cc: Antti Palosaari <crope@iki.fi>
Signed-off-by: Lukas Middendorf <kernel@tuxforce.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>