soundwire: sysfs: Constify static struct attribute_group

soundwire: sysfs: Constify static struct attribute_group

The only place sdw_slave_dev_attr_group is used is when its address is
passed to devm_device_add_group() which takes a pointer to const struct
attribute_group. Make it const to allow the compiler to put it in
read-only memory. This makes all attribute_group structs in the file
const. Done with the help of Coccinelle.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Link: https://lore.kernel.org/r/20210117221622.34315-1-rikard.falkeborn@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>