glu: fix two Clang warnings

This patch removes two Clang warnings in GLU:

The first one seems to be an actual bug in mapdesc.cc: Clang complains
that sizeof(dest) will return the size of REAL*[MAXCOORDS], instead of
the intended REAL[MAXCOORDS][MAXCOORDS]. The second one is just
cosmetic because Clang doesn't like extra parentheses.

NOTE: This is a candidate for the 8.0 branch

Reviewed-by: Brian Paul <brianp@vmware.com>