most: core: use function subsys_initcall()

This patch replaces function module_init() with subsys_initcall().
It is needed to ensure that the core module of the driver is
initialized before a component tries to register with the core. This
leads to a NULL pointer dereference if the driver is configured as
in-tree.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/1587741394-22021-1-git-send-email-christian.gromm@microchip.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/most/core.c

@@ -1483,7 +1483,7 @@ static void __exit most_exit(void)
 	ida_destroy(&mdev_id);
 }
 
-module_init(most_init);
+subsys_initcall(most_init);
 module_exit(most_exit);
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Christian Gromm <christian.gromm@microchip.com>");