fs_mgr: report errno string for __mount errors

Need to know why the mount failed.  clang_format adjustment.

Basically change LINFO to PINFO to cause the log message for the mount
report to be accompanied by a strerror(errno) message appended to the
end so that it is clear why the mount was rejected.

Test: manual
Bug: 63100799
Change-Id: Ic958299759befe5d5b11bdc95fea5d64cad86412