[PATCH bpf-next 2/2] selftests/bpf: Fix vmtest.sh getopts optstring

[Daniel Xu <dxu@xxxxxxxxx>]

Before, you could see the following errors:

```
$ ./vmtest.sh -j
./vmtest.sh: option requires an argument -- j
./vmtest.sh: line 357: OPTARG: unbound variable

$ ./vmtest.sh -z
./vmtest.sh: illegal option -- z
./vmtest.sh: line 357: OPTARG: unbound variable
```

Fix by adding ':' as first character of optstring. Reason is that
getopts requires ':' as the first character for OPTARG to be set in the
`?` and `:` error cases.

Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
---
 tools/testing/selftests/bpf/vmtest.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/vmtest.sh b/tools/testing/selftests/bpf/vmtest.sh
index 976ef7585b33..a29aa05ebb3e 100755
--- a/tools/testing/selftests/bpf/vmtest.sh
+++ b/tools/testing/selftests/bpf/vmtest.sh
@@ -333,7 +333,7 @@ main()
 	local exit_command="poweroff -f"
 	local debug_shell="no"
 
-	while getopts 'hskid:j:' opt; do
+	while getopts ':hskid:j:' opt; do
 		case ${opt} in
 		i)
 			update_image="yes"
-- 
2.37.1