trace/osnoise: Make interval u64 on osnoise_main

trace/osnoise: Make interval u64 on osnoise_main

kernel test robot reported:

  >> kernel/trace/trace_osnoise.c:966:3: warning: comparison of distinct
     pointer types ('typeof ((interval)) *' (aka 'long long *') and
     'uint64_t *' (aka 'unsigned long long *'))
     [-Wcompare-distinct-pointer-types]
                   do_div(interval, USEC_PER_MSEC);
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/asm-generic/div64.h:228:28: note: expanded from macro 'do_div'
           (void)(((typeof((n)) *)0) == ((uint64_t *)0));  \
                  ~~~~~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~

As interval cannot be negative because sample_period >= sample_runtime,
making interval u64 on osnoise_main() is enough to fix this problem.

Link: https://lkml.kernel.org/r/4ae1e7780563598563de079a3ef6d4d10b5f5546.1624872608.git.bristot@redhat.com
Fixes: bce29ac9ce0b ("trace: Add osnoise tracer")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>