ACPICA: exserial: don't forget to handle FFixedHW opregions for reading

[ Upstream commit 0f8af035 ]

The initial commit that introduced support for FFixedHW operation
regions did add a special case in the AcpiExReadSerialBus If, but
forgot to actually handle it inside the switch, so add the missing case
to prevent reads from failing with AE_AML_INVALID_SPACE_ID.

Link: https://github.com/acpica/acpica/pull/998


Fixes: ee64b827 ("ACPICA: Add support for FFH Opregion special context data")
Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Link: https://patch.msgid.link/20250401184312.599962-1-d-tatianin@yandex-team.ru


Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>