[PATCH] selftests/powerpc: Fix compiling error on tlbie_test due to newer gcc

["Desnes A. Nunes do Rosario" <desnesn@linux.ibm.com>]

Newer versions of GCC demand that the size of the string to be copied must
be explicitly smaller than the size of the destination. Thus, the NULL
char has to be taken into account on strncpy.

This will avoid the following compiling error:

  tlbie_test.c: In function 'main':
  tlbie_test.c:639:4: error: 'strncpy' specified bound 100 equals destination size [-Werror=stringop-truncation]
      strncpy(logdir, optarg, LOGDIR_NAME_SIZE);
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

Signed-off-by: Desnes A. Nunes do Rosario <desnesn@linux.ibm.com>
---
 tools/testing/selftests/powerpc/mm/tlbie_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/powerpc/mm/tlbie_test.c b/tools/testing/selftests/powerpc/mm/tlbie_test.c
index 9868a5ddd847..0d0aee462f8e 100644
--- a/tools/testing/selftests/powerpc/mm/tlbie_test.c
+++ b/tools/testing/selftests/powerpc/mm/tlbie_test.c
@@ -636,7 +636,7 @@ int main(int argc, char *argv[])
 			nrthreads = strtoul(optarg, NULL, 10);
 			break;
 		case 'l':
-			strncpy(logdir, optarg, LOGDIR_NAME_SIZE);
+			strncpy(logdir, optarg, LOGDIR_NAME_SIZE-1);
 			break;
 		case 't':
 			run_time = strtoul(optarg, NULL, 10);
-- 
2.21.0