edksetup.sh: Use bash variable $PWD instead of executing pwd command

This is a (very minor) optimization: `pwd` runs the command (even as a
built-in), whereas $PWD simply evaluates the value of the variable.

ALso, modern scripts should generally use $(...) to run commands,
instead of `...`.

Signed-off-by: Rebecca Cran <rebecca@bsdio.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Message-Id: <20190716165538.57960-1-rebecca@bsdio.com>

edksetup.sh

@@ -71,7 +71,7 @@ function SetWorkspace()
   #
   # Set $WORKSPACE
   #
-  export WORKSPACE=`pwd`
+  export WORKSPACE=$PWD
   return 0
 }