r300g: Fix uninitialized variable warnings in error path.

src/gallium/drivers/r300/r300_emit.c

@@ -512,6 +512,8 @@ void r300_emit_rs_state(struct r300_context* r300, unsigned size, void* state)
                     break;
                 default:
                     debug_printf("r300: Bad number of multisamples!\n");
+                    mspos0 = 0;
+                    mspos1 = 0;
                     break;
             }