md/raid5-ppl: Use atomic64_inc_return() in ppl_new_iounit()

Use atomic64_inc_return(&ref) instead of atomic64_add_return(1, &ref)
to use optimized implementation and ease register pressure around
the primitive for targets that implement optimized variant.

Signed-off-by: Uros Bizjak <[e-mail]>
Cc: Song Liu <[e-mail]>
Cc: Yu Kuai <[e-mail]>
Reviewed-by: Yu Kuai <[e-mail]>
Reviewed-by: Artur Paszkiewicz <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Song Liu <[e-mail]>

drivers/md/raid5-ppl.c

···
 	memset(pplhdr->reserved, 0xff, PPL_HDR_RESERVED);
 	pplhdr->signature = cpu_to_le32(ppl_conf->signature);
 
-	io->seq = atomic64_add_return(1, &ppl_conf->seq);
+	io->seq = atomic64_inc_return(&ppl_conf->seq);
 	pplhdr->generation = cpu_to_le64(io->seq);
 
 	return io;