cnss2: Fix minor issues related to runtime PM debugfs interface

pm_runtime_*() APIs may return positive number if device is already
active. Currently the positive number will be returned to upper layer
which will be considered a valid read count. If the number returned
is less then the command size, the rest of command will be re-parsed
again which results invalid command being printed which is confusing.
Hence only return it if it is a negative error code, otherwise just
return read count. Fix another place which may run into the same
situation. Also add missing info for runtime PM debugfs interface.

Change-Id: I7c53dc2cbe15164da816a479c77a202a3dfc4f93
Signed-off-by: Yue Ma <yuem@codeaurora.org>