pwm: pxa: Use module_platform_driver

Commit 76abbdde2d95a3807d0dc6bf9f84d03d0dbd4f3d

    pwm: Add sysfs interface

causes a kernel oops due to a null pointer dereference on PXA platforms.
This happens because the class added by the patch is registered in a
subsys_initcall (initcall4), but the pxa pwm driver is registered in
arch_initcall (initcall3). If the class is not registered before the
driver probe function runs, the oops occurs in device_add() when the
uninitialized pointers in struct class are dereferenced.  I don't see a
reason that the driver must be an arch_initcall, so this patch makes it
a regular module_platform_driver (initcall6), preventing the oops.

Signed-off-by: Mike Dunn <mikedunn@newsguy.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-pxa.c

@@ -182,16 +182,6 @@ static struct platform_driver pwm_driver = {
 	.id_table	= pwm_id_table,
 };
 
-static int __init pwm_init(void)
-{
-	return platform_driver_register(&pwm_driver);
-}
-arch_initcall(pwm_init);
-
-static void __exit pwm_exit(void)
-{
-	platform_driver_unregister(&pwm_driver);
-}
-module_exit(pwm_exit);
+module_platform_driver(pwm_driver);
 
 MODULE_LICENSE("GPL v2");