media: cec-pin: rename timer overrun variables

The cec pin timer overruns are measured in microseconds, but the variable
names include the millisecond symbol "ms". To avoid confusion, replace
"ms" with "us" in the variable names and printed status message.

Signed-off-by: Deborah Brouwer <deborahbrouwer3563@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>