tools: iio: make scale and offset files optional

Make scale and offset optional by adding -ENOENT check as not all
drivers implement them.
Signed-off-by: Joo Aun Saw <jasaw@dius.com.au>
Acked-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

tools/iio/iio_utils.c

@@ -487,7 +487,7 @@ int build_channel_array(const char *device_dir,
 						       device_dir,
 						       current->name,
 						       current->generic_name);
-			if (ret < 0)
+			if ((ret < 0) && (ret != -ENOENT))
 				goto error_cleanup_array;
 
 			ret = iioutils_get_param_float(&current->offset,
@@ -495,7 +495,7 @@ int build_channel_array(const char *device_dir,
 						       device_dir,
 						       current->name,
 						       current->generic_name);
-			if (ret < 0)
+			if ((ret < 0) && (ret != -ENOENT))
 				goto error_cleanup_array;
 
 			ret = iioutils_get_type(&current->is_signed,