selftests: kvm: Fix -Wformat warnings

Fixes the following warnings:

dirty_log_test.c: In function ‘help’:
dirty_log_test.c:216:9: warning: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 2 has type ‘int’ [-Wformat=]
  printf(" -i: specify iteration counts (default: %"PRIu64")\n",
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from include/test_util.h:18:0,
                 from dirty_log_test.c:16:
/usr/include/inttypes.h:105:34: note: format string is defined here
 # define PRIu64  __PRI64_PREFIX "u"
dirty_log_test.c:218:9: warning: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 2 has type ‘int’ [-Wformat=]
  printf(" -I: specify interval in ms (default: %"PRIu64" ms)\n",
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from include/test_util.h:18:0,
                 from dirty_log_test.c:16:
/usr/include/inttypes.h:105:34: note: format string is defined here
 # define PRIu64  __PRI64_PREFIX "u"

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>