iio: accel: msa311: Use correct header(s) instead of string_helpers.h

There is nothing from string_helpers.h used in the driver, correct
the header inclusion block accordingly.

Signed-off-by: Andy Shevchenko <[e-mail]>
Reviewed-by: Dmitry Rokosov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/accel/msa311.c

···
 #include <linux/pm.h>
 #include <linux/pm_runtime.h>
 #include <linux/regmap.h>
-#include <linux/string_helpers.h>
+#include <linux/string_choices.h>
 #include <linux/units.h>
 
 #include <linux/iio/buffer.h>