include/android_ab: move ab_select_slot() documentation to @ notation

include/android_ab: move ab_select_slot() documentation to @ notation

There are new function documentation requirements in U-Boot, so apply
these changes for android_ab.

Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Guillaume La Roque <glaroque@baylibre.com>
Signed-off-by: Dmitry Rokosov <ddrokosov@salutedevices.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> # vim3_android
Link: https://lore.kernel.org/r/20241017-android_ab_master-v5-1-43bfcc096d95@salutedevices.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>