[PATCH] iio: adc: ti_am335x_adc: Limit step_avg to valid range for gcc complains

[Pei Xiao]

FIELD_PREP() checks that a value fits into the available bitfield, add a
check for step_avg to fix gcc complains.

which gcc complains about:
  drivers/iio/adc/ti_am335x_adc.c: In function 'tiadc_step_config':
  include/linux/compiler_types.h:572:38: error: call to
'__compiletime_assert_491' declared with attribute error: FIELD_PREP: value
too large for the field include/linux/mfd/ti_am335x_tscadc.h:58:29: note:
in expansion of macro 'FIELD_PREP'
    #define STEPCONFIG_AVG(val) FIELD_PREP(GENMASK(4, 2), (val))
                                ^~~~~~~~~~
drivers/iio/adc/ti_am335x_adc.c:127:17: note: in expansion of macro 'STEPCONFIG_AVG'
	stepconfig = STEPCONFIG_AVG(ffs(adc_dev->step_avg[i]) - 1)

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202510102117.Jqxrw1vF-lkp@xxxxxxxxx/
Signed-off-by: Pei Xiao <xiaopei01@xxxxxxxxxx>
---
 drivers/iio/adc/ti_am335x_adc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
index 99f274adc870..45bdd57bfdc2 100644
--- a/drivers/iio/adc/ti_am335x_adc.c
+++ b/drivers/iio/adc/ti_am335x_adc.c
@@ -123,7 +123,7 @@ static void tiadc_step_config(struct iio_dev *indio_dev)
 
 		chan = adc_dev->channel_line[i];
 
-		if (adc_dev->step_avg[i])
+		if (adc_dev->step_avg[i] && adc_dev->step_avg[i] < STEPCONFIG_AVG_16)
 			stepconfig = STEPCONFIG_AVG(ffs(adc_dev->step_avg[i]) - 1) |
 				     STEPCONFIG_FIFO1;
 		else
-- 
2.25.1