hw/loongarch/boot: Use warn_report when no kernel filename

When we run “qemu-system-loongarch64 -qmp stdio -vnc none -S”,
we get an error message “Need kernel filename” and then we can't use qmp cmd to query some information.
So, we just throw a warning and then the cpus starts running from address VIRT_FLASH0_BASE.

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20241030012359.4040817-1-gaosong@loongson.cn>
diff --git a/hw/loongarch/boot.c b/hw/loongarch/boot.c
index cb66870..f258eef 100644
--- a/hw/loongarch/boot.c
+++ b/hw/loongarch/boot.c
@@ -278,7 +278,7 @@
 static void loongarch_direct_kernel_boot(struct loongarch_boot_info *info)
 {
     void *p, *bp;
-    int64_t kernel_addr = 0;
+    int64_t kernel_addr = VIRT_FLASH0_BASE;
     LoongArchCPU *lacpu;
     CPUState *cs;
 
@@ -286,8 +286,7 @@
         kernel_addr = load_kernel_info(info);
     } else {
         if(!qtest_enabled()) {
-            error_report("Need kernel filename\n");
-            exit(1);
+            warn_report("No kernel provided, booting from flash drive.");
         }
     }