[Yaffs] Trivial yportenv.h patch

To get the LINUX_VERSION_CODE macro (when building yaffs as a module) I
needed to apply the following trivial patch. I think yportenv is the
correct place to put it.

Cheers
Brad

Index: yportenv.h
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RCS file: /home/aleph1/cvs/yaffs/yportenv.h,v
retrieving revision 1.11
diff -r1.11 yportenv.h
38a39
> #include "linux/version.h"