SecurityPkg OpalPasswordDxe: Fix buffer overflow issue.

In current code, PSID is processed as string and the length is 0x20.
Current code only reserved 0x20 length buffer for it, no extra buffer
for the '\0'. When driver call UnicodeStrToAsciiStrS to convert PSID,
it search the '\0' for the end. So extra dirty data saved in PSID
info which caused PSID revert action failed. This patch reserved
extra 1 byte data for the '\0'.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Eric Dong <eric.dong@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>