rust/minijail: Fix cast to c_char. am: 11395a6982 am: 036c252f23 am: af243930d7 am: 23838c955e

Original change: https://android-review.googlesource.com/c/platform/external/minijail/+/1682968

Change-Id: I1659320e328a20de8daf3ffe523971b3c542b2be