genirq: Remove unnecessary memset() calls

sprintf() and snprintf() implementation of kernel guarantees that
its result is terminated with null byte if size is larger than 0. So we
don't need to call memset() at all.

Signed-off-by: Weongyo Jeong <weongyo.linux@gmail.com>
Link: http://lkml.kernel.org/r/1459451703-5744-1-git-send-email-weongyo.linux@gmail.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>