MdePkg-BaseLib: Fix PathCleanUpDirectories() error involving "\..\.."

MdePkg-BaseLib: Fix PathCleanUpDirectories() error involving "\..\.."

MdePkg-BaseLib: Fix PathCleanUpDirectories() error involving "\..\.."

The loop that removes "xxxx\..\" errs when multiple "\.." sequences are
in the path.  Before this change the code would modify a path like
"FS0:\efi\tools\..\.." to "FS0:\efi\\.." and then to "FS0:\efi\", but
the correct path is "FS0:\".

You can test the effect of this change in the shell by setting the
current directory to something like FS0:\efi\boot and then executing
the command "ls ..\..".  Before the change you will see the files in
the FS0:\efi directory; after the change, you will see the files in
the root directory of FS0:.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jim Dailey <jim_dailey@dell.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>