bcache: split combined if-condition code into separate ones

Split the combined '||' statements in if() check, to make the code easier
for debug.

Signed-off-by: Dongbo Cao <cdbdyx@163.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>