samples/bpf: Replace blk_account_io_done() with __blk_account_io_done()

Since commit be6bfe36 ("block: inline hot paths of blk_account_io_*()")
blk_account_io_*() become inline functions.

Signed-off-by: Rong Tao <rtoax@foxmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/tencent_1CC476835C219FACD84B6715F0D785517E07@qq.com