intel/fs: grab fail_msg from v32 instead of v16 when v32->run_cs fails

Looks like a copy/paste error. This patch prevents a segfault when
running the following on BDW:

    INTEL_DEBUG=no8,no16,do32 ./deqp-vk -n \
        dEQP-VK.subgroups.arithmetic.compute.subgroupmin_dvec4

For the curious, the message we're getting is:

    CS compile failed: Failure to register allocate.  Reduce number
    of live scalar values to avoid this.

Fixes: 864737ce6c ("i965/fs: Build 32-wide compute shader when needed.")
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

src/intel/compiler/brw_fs.cpp

@@ -8429,7 +8429,7 @@ brw_compile_cs(const struct brw_compiler *compiler, void *log_data,
       if (!v32->run_cs(min_dispatch_width)) {
          compiler->shader_perf_log(log_data,
                                    "SIMD32 shader failed to compile: %s",
-                                   v16->fail_msg);
+                                   v32->fail_msg);
          if (!v) {
             fail_msg =
                "Couldn't generate SIMD32 program and not "