We this to access task_is_booster().
ld.lld: error: undefined symbol: task_is_booster
>>> referenced by elevator.c:774 (../block/elevator.c:774)
>>> vmlinux.o:(elv_iosched_store)
>>> did you mean: task_is_booster
>>> defined in: vmlinux.o
Signed-off-by: Nahuel Gómez <nahuelgomez329@gmail.com>