iio: dac: stm32-dac: Replace open coded str_enable_disable()

Replace open coded str_enable_disable() in error message in
stm32_dac_set_enable_state().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220616220023.9894-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>