stddef: Fix kerndoc for sizeof_field() and offsetofend()

Adjust the comment styles so these are correctly identified as valid
kern-doc.
Signed-off-by: Kees Cook <keescook@chromium.org>

include/linux/stddef.h

@@ -20,7 +20,7 @@ enum {
 #endif
 
 /**
- * sizeof_field(TYPE, MEMBER)
+ * sizeof_field() - Report the size of a struct field in bytes
  *
  * @TYPE: The structure containing the field of interest
  * @MEMBER: The field to return the size of
@@ -28,7 +28,7 @@ enum {
 #define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
 
 /**
- * offsetofend(TYPE, MEMBER)
+ * offsetofend() - Report the offset of a struct field within the struct
  *
  * @TYPE: The type of the structure
  * @MEMBER: The member within the structure to get the end offset of