drm/i915: Free the returned object of acpi_evaluate_dsm()

drm/i915: Free the returned object of acpi_evaluate_dsm()

As per the comment on top of acpi_evaluate_dsm():

| * Evaluate device's _DSM method with specified GUID, revision id and
| * function number. Caller needs to free the returned object.

We should free the returned object of acpi_evaluate_dsm() to avoid memory
leakage. Otherwise the kmemleak splat will be triggered at boot time (if we
compile kernel with CONFIG_DEBUG_TEST_DRIVER_REMOVE=y).

Fixes: 8e55f99c510f ("drm/i915: Invoke another _DSM to enable MUX on HP Workstation laptops")
Cc: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210906033541.862-1-yuzenghui@huawei.com
(cherry picked from commit 149ac2e7ae1845191bd18b66a725392ac83a0c47)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>