ALSA: cs4281: Send the PCM period elapsed notification properly

ALSA: cs4281: Send the PCM period elapsed notification properly

As part of spin lock code cleanup using guard(), a new
variable (period_elapsed) was introduced. However this variable
is never set, causing period elapsed notification to be not sent.

Set the value of period_elapsed appropiately.

This issue was reported by static coverity analyzer.

Fixes: 7a5127c2c8a5a ("ALSA: cs4281: Use guard() for spin locks")
Signed-off-by: Chandra Mohan Sundar <chandramohan.explore@gmail.com>
Link: https://patch.msgid.link/20250906162158.564899-1-chandramohan.explore@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>