bcache: fix input overflow to cache set io_error_limit

c->error_limit is in type unsigned int, it is set via cache set sysfs
file io_error_limit. Inside the bcache code, input string is converted
by strtoul_or_return() and set the converted value to c->error_limit.

Because the converted value is unsigned long, and c->error_limit is
unsigned int, if the input is large enought, overflow will happen to
c->error_limit.

This patch uses sysfs_strtoul_clamp() to convert input string, and set
the range in [0, UINT_MAX] to avoid the potential overflow.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>