opp: Correct debug message in _opp_add_static_v2()

The debug message always prints rate=0 instead of a proper value, fix it.

Fixes: 6c591eec ("OPP: Add helpers for reading the binding properties")
Tested-by: Peter Geis <pgwipeout@gmail.com>
Tested-by: Nicolas Chauvet <kwizart@gmail.com>
Tested-by: Matt Merhar <mattmerhar@protonmail.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
[ Viresh: Added Fixes tag ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>