agx: make sure denorm flushing really happens

Backport-to: 25.1
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Mel Henning <mhenning@darkrefraction.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36147>

src/asahi/compiler/agx_nir_lower_fminmax.c

@@ -62,6 +62,8 @@ lower(nir_builder *b, nir_alu_instr *alu, void *data)
 
    if (could_be_denorm(src0) || could_be_denorm(src1)) {
       b->cursor = nir_after_instr(&alu->instr);
+      b->exact = true;
+
       nir_def *canonicalized = nir_fadd_imm(b, &alu->def, -0.0);
       nir_def_rewrite_uses_after(&alu->def, canonicalized,
                                  canonicalized->parent_instr);