iio: adc: stm32: make array stm32h7_adc_ckmodes_spec static

The array stm32h7_adc_ckmodes_spec does not need to be in global scope, so
make it static.

Cleans up sparse warning:
"symbol 'stm32h7_adc_ckmodes_spec' was not declared. Should it be static?"
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Acked-by: NFabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

drivers/iio/adc/stm32-adc-core.c

@@ -172,7 +172,7 @@ struct stm32h7_adc_ck_spec {
 	int div;
 };
 
-const struct stm32h7_adc_ck_spec stm32h7_adc_ckmodes_spec[] = {
+static const struct stm32h7_adc_ck_spec stm32h7_adc_ckmodes_spec[] = {
 	/* 00: CK_ADC[1..3]: Asynchronous clock modes */
 	{ 0, 0, 1 },
 	{ 0, 1, 2 },