rtla/utils: Use calloc and check the potential memory allocation failure

Replace malloc with calloc and add memory allocating check
of mon_cpus before used.

Link: https://lkml.kernel.org/r/20220615073348.6891-1-jianchunfu@cmss.chinamobile.com



Fixes: 7d0dc957 ("rtla/timerlat: Add --dma-latency option")
Signed-off-by: jianchunfu <jianchunfu@cmss.chinamobile.com>
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>