drm/i915/audio: be explicit about intel_wakeref_t conversions

Use explicit casts to convert between intel_wakeref_t and unsigned long,
to not rely on intel_wakeref_t underlying type remaining unsigned long,
allowing us to change it as needed. (And yes, this is indeed preparation
for changing the typedef for intel_wakeref_t.)

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/9d2a2c2399e70f36e0d68d88136ac688f02988fe.1726680898.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>