ACPI: BGRT: use static for BGRT_SHOW kobj_attribute defines

Smatch reports this repesentative issue:

bgrt.c:26:1: warning: symbol 'bgrt_attr_version' was not declared. Should it be static?

Similar for *status,type,xoffset,yoffset

These variables are defined with the BGRT_SHOW macro.

For the definition of bgrt_attr_##_name,
the storage-class specifier should be static.
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/bgrt.c

@@ -21,7 +21,7 @@ static struct kobject *bgrt_kobj;
 	{									\
 		return sysfs_emit(buf, "%d\n", bgrt_tab._member);		\
 	}									\
-	struct kobj_attribute bgrt_attr_##_name = __ATTR_RO(_name)
+	static struct kobj_attribute bgrt_attr_##_name = __ATTR_RO(_name)
 
 BGRT_SHOW(version, version);
 BGRT_SHOW(status, status);