iio:accel:bmc150: Mark structure __maybe_unused as only needed with for pm ops.

If CONFIG_PM not set then clang warns this structure is unused.
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/20211128172445.2616166-12-jic23@kernel.org

drivers/iio/accel/bmc150-accel-core.c

@@ -170,7 +170,7 @@ static const struct {
 				     {1000, 0, 0x0E},
 				     {2000, 0, 0x0F} };
 
-static const struct {
+static __maybe_unused const struct {
 	int bw_bits;
 	int msec;
 } bmc150_accel_sample_upd_time[] = { {0x08, 64},