HID: hid-sensor-hub: Allow parallel synchronous reads

Current implementation only allows one outstanding synchronous read.
This is a performance hit when user mode is requesting raw reads
of sensor attributes on multiple sensors together.
This change changes the mutex lock to per hid sensor hub device instead
of global lock. Although request to hid sensor hub is serialized, there
can be multiple outstanding read requests pending for responses via
hid reports.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>