maple: make maple_bus_type static and const

There is no need to export maple_bus_type as no one uses it outside of
maple.c, so make it static, AND make it const as it can be read-only as
no one modifies it.

Cc: Yoshinori Sato <[e-mail]>
Cc: Rich Felker <[e-mail]>
Cc: John Paul Adrian Glaubitz <[e-mail]>
Cc: <[e-mail]>
Link: https://lore.kernel.org/r/2023121918-rejoicing-frostlike-d976@gregkh
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/sh/maple/maple.c

···
 static bool checked[MAPLE_PORTS];
 static bool empty[MAPLE_PORTS];
 static struct maple_device *baseunits[MAPLE_PORTS];
+static const struct bus_type maple_bus_type;
 
 /**
  * maple_driver_register - register a maple driver
···
 /*
  * maple_bus_type - core maple bus structure
  */
-struct bus_type maple_bus_type = {
+static const struct bus_type maple_bus_type = {
 	.name = "maple",
 	.match = maple_match_bus_driver,
 };
-EXPORT_SYMBOL_GPL(maple_bus_type);
 
 static struct device maple_bus = {
 	.init_name = "maple",

include/linux/maple.h

···
 #include <mach/maple.h>
 
 struct device;
-extern struct bus_type maple_bus_type;
 
 /* Maple Bus command and response codes */
 enum maple_code {