Fix some cmake syntax errors

I'm seeing the following warnings:

````
CMake Warning (dev) in CMakeLists.txt:
  Syntax Warning in cmake code at
    /builddir/build/BUILD/netcdf-c-4.3.1-rc2/CMakeLists.txt:360:56
  Argument not separated from preceding token by whitespace.

CMake Warning (dev) at CMakeLists.txt:91 (FIND_PACKAGE):
  Syntax Warning in cmake code at
    /builddir/build/BUILD/netcdf-c-4.3.1-rc2/cmake/modules/FindMakeDist.cmake:202:40
  Argument not separated from preceding token by whitespace.
````

This commit fixes those.