dm vdo indexer: prevent unterminated string warning

Fix array initialization that triggers a warning:

error: initializer-string for array of ‘unsigned char’ is too long
 [-Werror=unterminated-string-initialization]

Signed-off-by: Chung Chung <cchung@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>