fs/buffer.c: fix use true/false for bool type

Use true/false for bool return type of has_bh_in_lru().

Link: http://lkml.kernel.org/r/20191029040529.GA7625@saurav
Signed-off-by: Saurav Girepunje <saurav.girepunje@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>