blk-iocost: fix divide by 0 error in calc_lcoefs()

In the Linux kernel, the following vulnerability has been resolved:

blk-iocost: fix divide by 0 error in calc_lcoefs()

echo max of u64 to cost.model can cause divide by 0 error.

# echo 8:0 rbps=18446744073709551615 > /sys/fs/cgroup/io.cost.model

divide error: 0000 [#1] PREEMPT SMP

RIP: 0010:calc_lcoefs+0x4c/0xc0

Call Trace:

<TASK>

ioc_refresh_params+0x2b3/0x4f0

ioc_cost_model_write+0x3cb/0x4c0

? _copy_from_iter+0x6d/0x6c0

? kernfs_fop_write_iter+0xfc/0x270

cgroup_file_write+0xa0/0x200

kernfs_fop_write_iter+0x17d/0x270

vfs_write+0x414/0x620

ksys_write+0x73/0x160

__x64_sys_write+0x1e/0x30

do_syscall_64+0x35/0x80

entry_SYSCALL_64_after_hwframe+0x63/0xcd

calc_lcoefs() uses the input value of cost.model in DIV_ROUND_UP_ULL,

overflow would happen if bps plus IOC_PAGE_SIZE is greater than

ULLONG_MAX, it can cause divide by 0 error.

Fix the problem by setting basecost