PM: <linux/device.h>: fix @em_pd kernel-doc warning

PM: <linux/device.h>: fix @em_pd kernel-doc warning

Fix kernel-doc warning in <linux/device.h>:

../include/linux/device.h:613: warning: Function parameter or member 'em_pd' not described in 'device'

Fixes: 1bc138c62295 ("PM / EM: add support for other devices than CPUs in Energy Model")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://lore.kernel.org/r/d97f40ad-3033-703a-c3cb-2843ce0f6371@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>