iio:accel:kxcjk-1013: Mark struct __maybe_unused to avoid warning.

This structure is only used in PM ops, so may not be used depending
on build configuration.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20211128172445.2616166-13-jic23@kernel.org

drivers/iio/accel/kxcjk-1013.c

@@ -315,7 +315,7 @@ static const char *const kxtf9_samp_freq_avail =
  "25 50 100 200 400 800";
 
 /* Refer to section 4 of the specification */
-static const struct {
+static __maybe_unused const struct {
  int odr_bits;
  int usec;
 } odr_start_up_times[KX_MAX_CHIPS][12] = {