MdeModulePkg/UdfDxe: Remove negative comparison of unsigned number

MdeModulePkg/UdfDxe: Remove negative comparison of unsigned number

This patch gets rid of a negative comparison of an UINT64 type (Offset)
as it'll never evaluate to true.

Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Dandan Bi <dandan.bi@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Reported-by: Star Zeng <star.zeng@intel.com>
Signed-off-by: Paulo Alcantara <pcacjr@zytor.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>