OPP: Initialize scope-based pointers inline

OPP: Initialize scope-based pointers inline

Uninitialized pointers with `__free` attribute can cause undefined
behaviour as the memory allocated to the pointer is freed automatically
when the pointer goes out of scope.

The OPP core doesn't have any bugs related to this as of now, but it is
better to initialize pointers marked with `__free` attribute at
declaration to simplify the code and ensure proper scope-based cleanup.

Reported-by: Joe Perches <joe@perches.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>