driver core: fix documentation of request_firmware_nowait

request_firmware_nowait declares it can be called in non-sleep contexts,
but kthead_run called by request_firmware_nowait may sleep. So fix its
documentation and comment to make callers clear about it.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 2d296b7..2427702 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -617,8 +617,9 @@
  * @cont: function will be called asynchronously when the firmware
  *	request is over.
  *
- *	Asynchronous variant of request_firmware() for contexts where
- *	it is not possible to sleep.
+ *	Asynchronous variant of request_firmware() for user contexts where
+ *	it is not possible to sleep for long time. It can't be called
+ *	in atomic contexts.
  **/
 int
 request_firmware_nowait(