MdeModulePkg/Ufs: Set 'Data Segment Length' field for Write Descriptor

According to the Universal Flash Storage (UFS) Version 2.1 (JESD220C) spec
Section 10.7.8.5, the DATA SEGMENT LENGTH field of the UPIU shall also be
set to number of descriptor bytes to write.

The origin codes miss the above operation.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>