src/dio-offsets.c: fix compiler error of open()

The blktests build CI reported the error below:

 gcc  -O2 -Wall -Wshadow -Werror  -DHAVE_LINUX_BLKZONED_H  -o dio-offsets dio-offsets.c
In file included from /usr/include/fcntl.h:342,
                 from dio-offsets.c:14:
In function ‘open’,
    inlined from ‘init_args’ at dio-offsets.c:43:12,
    inlined from ‘main’ at dio-offsets.c:711:2:
/usr/include/x86_64-linux-gnu/bits/fcntl2.h:50:11: error: call to ‘__open_missing_mode’ declared with attribute error: open with O_CREAT or O_TMPFILE in second argument needs 3 arguments
   50 |           __open_missing_mode ();
      |           ^~~~~~~~~~~~~~~~~~~~~~

To avoid the error, remove the O_CREAT flag from the open() call. The
flag should not be necessary because the open target file is the test
target block device file which should exist.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>

Author: kawasaki

src/dio-offsets.c

@@ -40,7 +40,7 @@ static int test_fd;
 
 static void init_args(char **argv)
 {
-	test_fd = open(argv[1], O_RDWR | O_CREAT | O_TRUNC | O_DIRECT);
+	test_fd = open(argv[1], O_RDWR | O_TRUNC | O_DIRECT);
 	if (test_fd < 0)
 		err(errno, "%s: failed to open %s", __func__, argv[1]);