linux: Fix definition of try_to_freeze()

The new definition causes a build failure on some boards, such as
vexpress_ca9x4

Use a static inline function to resolve this.

Signed-off-by: Simon Glass <simon.glass@canonical.com>

include/linux/freezer.h

@@ -8,7 +8,8 @@
 #define _LINUX_FREEZER_H
 
 #define set_freezable()			do { } while (0)
-#define try_to_freeze()			do { } while (0)
+
+static inline int try_to_freeze(void) { return 0; }
 #define freezing(task)			({ (void)(task); 0; })
 #define frozen(task)			({ (void)(task); 0; })
 #define freezable_schedule()		do { } while (0)