iio: ssp_sensors: cleanup codestyle warning

Reported by checkpatch:
FILE: drivers/iio/common/ssp_sensors/ssp_dev.c

WARNING: Prefer __packed over __attribute__((__packed__))
+} __attribute__((__packed__));

Signed-off-by: Sanjay Chitroda <sanjayembeddedse@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Author: sanjay-embedded

drivers/iio/common/ssp_sensors/ssp_dev.c

@@ -28,7 +28,7 @@ struct ssp_instruction {
 	__le32 a;
 	__le32 b;
 	u8 c;
-} __attribute__((__packed__));
+} __packed__;
 
 static const u8 ssp_magnitude_table[] = {110, 85, 171, 71, 203, 195, 0, 67,
 	208, 56, 175, 244, 206, 213, 0, 92, 250, 0, 55, 48, 189, 252, 171,