cnss: Clear runtime_error flag when exit runtime PM feature

Clear the runtime_error flag so that runtime PM status can be set to
active when exit the feature. This makes sure that next time it is
able to start freshly.

Change-Id: I16d38d436a40e3538f174e7eb71f1c5f8c72d9f3
CRs-fixed: 893516
Signed-off-by: Yue Ma <yuem@codeaurora.org>