staging: fieldbus: make fieldbus_class constant

Since commit 43a7206b0963 ("driver core: class: make class_register() take
a const *"), the driver core allows for struct class to be in read-only
memory, so move the fieldbus_class structure to be declared at build time
placing it into read-only memory, instead of having to be dynamically
allocated at boot time.

Cc: Greg Kroah-Hartman <[e-mail]>
Suggested-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: "Ricardo B. Marliere" <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/fieldbus/dev_core.c

···
 };
 __ATTRIBUTE_GROUPS(fieldbus);
 
-static struct class fieldbus_class = {
+static const struct class fieldbus_class = {
 	.name =		"fieldbus_dev",
 	.dev_groups =	fieldbus_groups,
 };