When the ovsdb library pkgconfig changes were introduced, they placed
generated output in the src directory.  This is incorrect, however, as
the output files should actually be placed in the build directory.  It
is only seen when running `make distcheck` after enabling shared
libraries (ex: `./configure --enable-shared`).

Fixes: commit e72e07a9

 ("lib: Add support for pkgconfig for libovsdb.")
Signed-off-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>