platform/surface: aggregator: avoid clang -Wconstant-conversion warning

platform/surface: aggregator: avoid clang -Wconstant-conversion warning

Clang complains about the assignment of SSAM_ANY_IID to
ssam_device_uid->instance:

drivers/platform/surface/surface_aggregator_registry.c:478:25: error: implicit conversion from 'int' to '__u8' (aka 'unsigned char') changes value from 65535 to 255 [-Werror,-Wconstant-conversion]
        { SSAM_VDEV(HUB, 0x02, SSAM_ANY_IID, 0x00) },
        ~                      ^~~~~~~~~~~~
include/linux/surface_aggregator/device.h:71:23: note: expanded from macro 'SSAM_ANY_IID'
 #define SSAM_ANY_IID            0xffff
                                ^~~~~~
include/linux/surface_aggregator/device.h:126:63: note: expanded from macro 'SSAM_VDEV'
        SSAM_DEVICE(SSAM_DOMAIN_VIRTUAL, SSAM_VIRTUAL_TC_##cat, tid, iid, fun)
                                                                     ^~~
include/linux/surface_aggregator/device.h:102:41: note: expanded from macro 'SSAM_DEVICE'
        .instance = ((iid) != SSAM_ANY_IID) ? (iid) : 0,                        \
                                               ^~~

The assignment doesn't actually happen, but clang checks the type limits
before checking whether this assignment is reached. Replace the ?:
operator with a __builtin_choose_expr() invocation that avoids the
warning for the untaken part.

Fixes: eb0e90a82098 ("platform/surface: aggregator: Add dedicated bus and device type")
Cc: platform-driver-x86@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Maximilian Luz <luzmaximilian@gmail.com>
Link: https://lore.kernel.org/r/20210514200453.1542978-1-arnd@kernel.org
Signed-off-by: Hans de Goede <hdegoede@redhat.com>