compiler: avoid 'unused variable' warnings

compiler: avoid 'unused variable' warnings

1. nir/nir_lower_vars_to_ssa.c:691:21: warning:
       unused variable ‘var’
       nir_variable *var = path->path[0]->var;

v2: Changes for some part of 'may be used uninitialized'
    warnings were removed, seems like it is a compiler issue.
        ( Eric Engestrom <eric.engestrom@intel.com> )
    Possible like this one:
    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46684
    This issue is flagged as duplicate but an
    original one is not closed yet.

Signed-off-by: Andrii Simiklit <andrii.simiklit@globallogic.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>