regulator: event: Ensure atomicity for sequence number

Previously, the sequence number in the regulator event subsystem was
updated without atomic operations, potentially leading to race
conditions. This commit addresses the issue by making the sequence
number atomic.

Signed-off-by: Naresh Solanki <naresh.solanki@9elements.com>
Link: https://msgid.link/r/20240104141314.3337037-1-naresh.solanki@9elements.com


Signed-off-by: Mark Brown <broonie@kernel.org>