MdeModulePkg UfsPassThru: ASSERT if params are NULL in SignalCallerEvent

MdeModulePkg UfsPassThru: ASSERT if params are NULL in SignalCallerEvent

In function SignalCallerEvent(), 'Private' and 'TransReq' are dereferenced
before NULL checking.

Since the function assumes that both 'Private' and 'TransReq' passed in
are not NULL pointer, this commit will add an ASSERT to make sure the
above assumption is satisfied.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19266 6f19259b-4bc3-4df7-8a09-765794883524