tools/testing/selftests/vm/split_huge_page_test.c: fix application of sizeof to pointer

The coccinelle check report:

  ./tools/testing/selftests/vm/split_huge_page_test.c:344:36-42:
  ERROR: application of sizeof to pointer

Use "strlen" to fix it.

Link: https://lkml.kernel.org/r/20211012030116.184027-1-davidcomponentone@gmail.comSigned-off-by: David Yang <davidcomponentone@gmail.com>
Reported-by: Zeal Robot <zealci@zte.com.cn>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/split_huge_page_test.c

@@ -341,7 +341,7 @@ void split_file_backed_thp(void)
 	}
 
 	/* write something to the file, so a file-backed THP can be allocated */
-	num_written = write(fd, tmpfs_loc, sizeof(tmpfs_loc));
+	num_written = write(fd, tmpfs_loc, strlen(tmpfs_loc) + 1);
 	close(fd);
 
 	if (num_written < 1) {