Utilities: Fix local printf issue.

The bug can be reproduced by using a format that do not have
the width.prec specified after a format that have the width.prec
specified. The second formatted output will be wrong.
The root cause is AcpiUtVsnprintf() doesn't reset the specifiers to the default values.

This patch fixes this issue. BZ 1094. Reported by Yizhe Wang, fixed by Lv Zheng.