MdePkg SmmMemLib: Remove ASSERT in SmmIsBufferOutsideSmmValid

MdePkg SmmMemLib: Remove ASSERT in SmmIsBufferOutsideSmmValid

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=577

Currently the SmmIsBufferOutsideSmmValid() function in SmmMemLib.c will
ASSERT in certain conditions. Since this function is a "test" function,
it should not be making decisions on how to handle a failure.
Handling a failure should be left to the caller.

This patch is to remove ASSERT(FALSE) at line 178 of SmmMemLib.c.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Bret Barkelew <bret.barkelew@microsoft.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>