drm/imagination: Discard pm_runtime_put() return value

drm/imagination: Discard pm_runtime_put() return value

The Imagination DRM driver defines pvr_power_put() to pass the return
value of pm_runtime_put() to the caller, but then it never uses the
return value of pvr_power_put().

Modify pvr_power_put() to discard the pm_runtime_put() return value and
change its return type to void.

No intentional functional impact.

This will facilitate a planned change of the pm_runtime_put() return
type to void in the future.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Matt Coster <matt.coster@imgtec.com>
Link: https://patch.msgid.link/8642685.T7Z3S40VBb@rafael.j.wysocki