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/Documentation/firmware_class/README b/Documentation/firmware_class/README
index c3480aa..7eceaff 100644
--- a/Documentation/firmware_class/README
+++ b/Documentation/firmware_class/README
@@ -77,7 +77,8 @@
    seconds for the whole load operation.
 
  - request_firmware_nowait() is also provided for convenience in
-   non-user contexts.
+   user contexts to request firmware asynchronously, but can't be called
+   in atomic contexts.
 
 
  about in-kernel persistence: