MdeModulePkg/Ufs: Fix UFS flag read from Query Resp UPIU

MdeModulePkg/Ufs: Fix UFS flag read from Query Resp UPIU

As per UFS spec, flag value is stored in the 'last byte' of value
field. Existing code is attempting to read first byte.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2208

Test: Verified the Fix by sending command to set fPowerOnWPEn flag
and then reading it to verify the set value.

Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Sachin Agrawal <sachin.agrawal@intel.com>
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>