ShellPkg/Debug1CommandsLib: Fix bugs in func DisplaySysEventLogData

ShellPkg/Debug1CommandsLib: Fix bugs in func DisplaySysEventLogData

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1498

This patch fix following bugs in func DisplaySysEventLogData:
1. Log increment (Log = (LOG_RECORD_FORMAT *) (LogData + Offset);)
should happened in the end of while loop, not in the very beginning.
2. DisplaySELTypes function should be used in while loop instead of
DisplaySELVarDataFormatType.

Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Zhichao Gao <zhichao.gao@intel.com>
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Zhichao Gao <zhichao.gao@intel.com>