edksetup.bat: Fixed corrupts CYGWIN_HOME

edksetup.bat: Fixed corrupts CYGWIN_HOME

The .BAT file checks for existance of the directory c:\cygwin and,
if it exists, always resets CYGWIN_HOME to that path.
That means that if CYGWIN_HOME is set to say c:\cygwin64, it gets corrupted.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
Reviewed-by Yingke Liu <yingke.d.liu@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15254 6f19259b-4bc3-4df7-8a09-765794883524