timer: Fix two mistakes in callback conversions

Two errors found their way into the timer callback conversions that
weren't noticed with x86 allmodconfig.

Reported-by: kernel test robot <lkp@01.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20171005171035.GA34831@beast