nir/ttn: Silence some warnings at -Og

../src/gallium/auxiliary/nir/tgsi_to_nir.c: In function ‘ttn_mem’:
   ../src/gallium/auxiliary/nir/tgsi_to_nir.c:1724:15: warning: ‘op’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    1724 |       instr = nir_intrinsic_instr_create(b->shader, op);
   ../src/gallium/auxiliary/nir/tgsi_to_nir.c:1697:15: warning: ‘op’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    1697 |       instr = nir_intrinsic_instr_create(b->shader, op);

Add some more unreachable() to make this go away.

Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8724>

src/gallium/auxiliary/nir/tgsi_to_nir.c

@@ -1709,6 +1709,8 @@ ttn_mem(struct ttn_compile *c, nir_alu_dest dest, nir_ssa_def **src)
       case TGSI_OPCODE_STORE:
          op = nir_intrinsic_store_ssbo;
          break;
+      default:
+         unreachable("unexpected buffer opcode");
       }
 
       add_ssbo_var(c, resource_index);
@@ -1738,6 +1740,8 @@ ttn_mem(struct ttn_compile *c, nir_alu_dest dest, nir_ssa_def **src)
       case TGSI_OPCODE_STORE:
          op = nir_intrinsic_image_deref_store;
          break;
+      default:
+         unreachable("unexpected file opcode");
       }
 
       instr = nir_intrinsic_instr_create(b->shader, op);