ALSA: seq: Simplify snd_seq_kernel_client_enqueue() helper

We have two helpers for queuing a sequencer event from the kernel
client, and both are used only from OSS sequencer layer without any
hop and atomic set.  Let's simplify and unify two helpers into one.

No functional change, just a call pattern change.

Signed-off-by: Takashi Iwai <tiwai@suse.de>