m4/gst-check.m4: I know Thomas will kill me but this ifelse statement seems incorrect as it is always setting require...

Original commit message from CVS:
2005-10-17  Julien MOUTTE  <julien@moutte.net>

* m4/gst-check.m4: I know Thomas will kill me but this
ifelse statement seems incorrect as it is always setting
required to "yes". With this one it seems to work. Fixes
build of gst-plugins-base on my setup where gstreamer-check
is definitely not present/required.