ALSA: msnd: Optimize / harden DSP and MIDI loops

ALSA: msnd: Optimize / harden DSP and MIDI loops

commit 20e2b791796bd68816fa115f12be5320de2b8021 upstream.

The ISA msnd drivers have loops fetching the ring-buffer head, tail
and size values inside the loops.  Such codes are inefficient and
fragile.

This patch optimizes it, and also adds the sanity check to avoid the
endless loops.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=196131
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=196133
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: grygorii tertychnyi <gtertych@cisco.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>