misc: sgi-gru: Convert from atomic_t to refcount_t on gru_thread_state->ts_refcnt

misc: sgi-gru: Convert from atomic_t to refcount_t on gru_thread_state->ts_refcnt

refcount_t type and corresponding API can protect refcounters from
accidental underflow and overflow and further use-after-free situations.

Acked-by: Dimitri Sivanich <sivanich@hpe.com>
Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Link: https://lore.kernel.org/r/1626517043-42696-1-git-send-email-xiyuyang19@fudan.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>