counter: chrdev: fix getting array extensions

counter: chrdev: fix getting array extensions

When trying to watch a component array extension, and the array isn't the
first extended element, it fails as the type comparison is always done on
the 1st element. Fix it by indexing the 'ext' array.

Example on a dummy struct counter_comp:
static struct counter_comp dummy[] = {
	COUNTER_COMP_DIRECTION(..),
	...,
	COUNTER_COMP_ARRAY_CAPTURE(...),
};
static struct counter_count dummy_cnt = {
	...
	.ext = dummy,
	.num_ext = ARRAY_SIZE(dummy),
}

Currently, counter_get_ext() returns -EINVAL when trying to add a watch
event on one of the capture array element in such example.

Fixes: d2011be1e22f ("counter: Introduce the COUNTER_COMP_ARRAY component type")
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20230829134029.2402868-2-fabrice.gasnier@foss.st.com
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>