blk-throttle: Set BIO_THROTTLED when bio has been throttled

1.In current process, all bio will set the BIO_THROTTLED flag
after __blk_throtl_bio().

2.If bio needs to be throttled, it will start the timer and
stop submit bio directly. Bio will submit in
blk_throtl_dispatch_work_fn() when the timer expires.But in
the current process, if bio is throttled. The BIO_THROTTLED
will be set to bio after timer start. If the bio has been
completed, it may cause use-after-free blow.

BUG: KASAN: use-after-free in blk_throtl_bio+0x12f0/0x2c70
Read of size 2 at addr ffff88801b8902d4 by task fio/26380

 dump_stack+0x9b/0xce
 print_address_description.constprop.6+0x3e/0x60
 kasan_report.cold.9+0x22/0x3a
 blk_throtl_bio+0x12f0/0x2c70
 submit_bio_checks+0x701/0x1550
 submit_bio_noacct+0x83/0xc80
 submit_bio+0xa7/0x330
 mpage_readahead+0x380/0x500
 read_pages+0x1c1/0xbf0
 page_cache_ra_unbounded+0x471/0x6f0
 do_page_cache_ra+0xda/0x110
 ondemand_readahead+0x442/0xae0
 page_cache_async_ra+0x210/0x300
 generic_file_buffered_...