pwm: Make use of a symbol namespace for the core

Define all pwm core's symbols in the namespace "PWM". The necessary
module import statement is just added to the main header, this way every
file that knows about the public functions automatically has this
namespace available.

Thanks to Biju Das for pointing out a cut'n'paste failure in my initial
patch.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20240607160012.1206874-2-u.kleine-koenig@baylibre.comSigned-off-by: Uwe Kleine-König <ukleinek@kernel.org>

drivers/pwm/core.c

@@ -6,6 +6,8 @@
  * Copyright (C) 2011-2012 Avionic Design GmbH
  */
 
+#define DEFAULT_SYMBOL_NAMESPACE PWM
+
 #include <linux/acpi.h>
 #include <linux/module.h>
 #include <linux/idr.h>

include/linux/pwm.h

@@ -4,9 +4,12 @@
 
 #include <linux/device.h>
 #include <linux/err.h>
+#include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/of.h>
 
+MODULE_IMPORT_NS(PWM);
+
 struct pwm_chip;
 
 /**