Compiler Attributes: counted_by: fixup clang URL

The URL in question 404 now, fix it up (and switch to github).
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/b7babeb9c5b14af9189f0d6225673e6e9a8f4ad3.1704855496.git.senozhatsky@chromium.orgSigned-off-by: Miguel Ojeda <ojeda@kernel.org>

include/linux/compiler_attributes.h

@@ -99,7 +99,7 @@
  * Optional: only supported since clang >= 18
  *
  *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
- * clang: https://reviews.llvm.org/D148381
+ * clang: https://github.com/llvm/llvm-project/pull/76348
  */
 #if __has_attribute(__counted_by__)
 # define __counted_by(member)		__attribute__((__counted_by__(member)))