Fix type signature for CMIUtilString::IsAllValidAlphaAndNumeric.

This should take a "const char*" not a "char &".

Summary:
Fix type signature for CMIUtilString::IsAllValidAlphaAndNumeric.

This passes the MI tests on Mac OS X.

Reviewers: ki.stfu, abidh, domipheus

Subscribers: lldb-commits-list

Differential Revision: http://reviews.llvm.org/D10906

llvm-svn: 241322