Revert "exfat: AIO Optimization compatibility fixup"

This reverts commit 8f40c744cb3f8c0b19b0f21bd26abdf6847e7d34.
introduce for_each_thread() to replace the buggy while_each_thread() …
…(fix)

fix a merge derp. pointed out by neobuddy89

Signed-off-by: Paul Reioux <reioux@gmail.com>
FIX: to allow previous commit cb21b92e9cc467e1ac3fc10023fba3f093759967