counter: stm32-timer-cnt: rename counter

The STM32 timer may count on various sources or channels. The counter
isn't specifically counting on channe1 1. So rename it to avoid a
confusion.

Reviewed-by: William Breathitt Gray <william.gray@linaro.org>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20240307133306.383045-3-fabrice.gasnier@foss.st.com


Signed-off-by: William Breathitt Gray <william.gray@linaro.org>