etnaviv: fix compile warnings in release build

etnaviv: fix compile warnings in release build

[27/31] Compiling C object 'src/gallium/drivers/etnaviv/df32d18@@etnaviv@sta/etnaviv_compiler_nir.c.o'.
In file included from ../../src/gitlab_mesa/src/gallium/drivers/etnaviv/etnaviv_compiler_nir.c:552:
../../src/gitlab_mesa/src/gallium/drivers/etnaviv/etnaviv_compiler_nir_emit.h: In function 'ra_assign':
../../src/gitlab_mesa/src/gallium/drivers/etnaviv/etnaviv_compiler_nir_emit.h:903:9: warning: unused variable 'ok' [-Wunused-variable]
    bool ok = ra_allocate(g);
         ^~
../../src/gitlab_mesa/src/gallium/drivers/etnaviv/etnaviv_compiler_nir.c: In function 'etna_compile_shader_nir':
../../src/gitlab_mesa/src/gallium/drivers/etnaviv/etnaviv_compiler_nir.c:663:9: warning: unused variable 'ok' [-Wunused-variable]
    bool ok = emit_shader(c->nir, &options, &v->num_temps, &num_consts);
         ^~

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Jonathan Marek <jonathan@marek.ca>