devres: Improve devm_kasprintf()/kvasprintf() support

  - Add devm_kasprintf()/kvasprintf(), introduced by commit
    75f2a4ead5d5890ada9c2663a70fb58613c0d9f2 ("devres: Add
    devm_kasprintf and devm_kvasprintf API"), to
    Documentation/driver-model/devres.txt,
  - Improve kernel doc: the string is not an existing formatted string,
    but is formatted into the newly-allocated buffer,
  - Add a __printf() annotation to devm_kasprintf(), so the compiler
    will verify the format string argument types.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/device.h b/include/linux/device.h
index 43d183a..a608e23 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -607,8 +607,8 @@
 extern void *devm_kmalloc(struct device *dev, size_t size, gfp_t gfp);
 extern char *devm_kvasprintf(struct device *dev, gfp_t gfp, const char *fmt,
 			     va_list ap);
-extern char *devm_kasprintf(struct device *dev, gfp_t gfp,
-			    const char *fmt, ...);
+extern __printf(3, 4)
+char *devm_kasprintf(struct device *dev, gfp_t gfp, const char *fmt, ...);
 static inline void *devm_kzalloc(struct device *dev, size_t size, gfp_t gfp)
 {
 	return devm_kmalloc(dev, size, gfp | __GFP_ZERO);