Uniform block members do not get a uniform location, since they
cannot be set (or get) through regular glUniform* functions. These
are instead always set using uniform buffers.

Bug chromium:763675,chromium:763698,chromium:771639

Change-Id: Icf65eba3faab420c63f70af66f828a786e3fc446
Reviewed-on: https://swiftshader-review.googlesource.com/13068Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>