tests : clock_control: clean "STM32_SRC_SYSCLK"

clean up usage of usage "#ifdef STM32_SRC_SYSCLK"
and code under the "#else" from
test_stm32_clock_configuration_adc.c.

Signed-off-by: Khaoula Bidani <khaoula.bidani-ext@st.com>
1 file changed