overflow: Correct check_shl_overflow() comment

A 'false' return means the value was safely set, so the comment should
say 'true' for when it is not considered safe.

Cc: Jason Gunthorpe <jgg@ziepe.ca>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Fixes: 0c668477 ("overflow.h: Add arithmetic shift helper")
Link: https://lore.kernel.org/r/20210401160629.1941787-1-kbusch@kernel.org

include/linux/overflow.h

@@ -235,7 +235,7 @@ static inline bool __must_check __must_check_overflow(bool overflow)
  * - 'a << s' sets the sign bit, if any, in '*d'.
  *
  * '*d' will hold the results of the attempted shift, but is not
- * considered "safe for use" if false is returned.
+ * considered "safe for use" if true is returned.
  */
 #define check_shl_overflow(a, s, d) __must_check_overflow(({		\
 	typeof(a) _a = a;						\