BUG_ON conversion for fs/aio.c

This patch converts a if () BUG(); construct to BUG_ON();
which occupies less space, uses unlikely and is safer when
BUG() is disabled.

Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

diff --cc fs/aio.c
Simple merge