sandbox: mark sandbox_exit() as no return.

Fix a -Wimplicit-fallthrough warning in sandbox_sysreset_request().

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/cpu/cpu.c b/arch/sandbox/cpu/cpu.c
index 248d17a..5149633 100644
--- a/arch/sandbox/cpu/cpu.c
+++ b/arch/sandbox/cpu/cpu.c
@@ -31,7 +31,7 @@
 unsigned long map_len;
 #endif
 
-void sandbox_exit(void)
+void __noreturn sandbox_exit(void)
 {
 	/* Do this here while it still has an effect */
 	os_fd_restore();
diff --git a/arch/sandbox/include/asm/u-boot-sandbox.h b/arch/sandbox/include/asm/u-boot-sandbox.h
index 9eb1932..e702774 100644
--- a/arch/sandbox/include/asm/u-boot-sandbox.h
+++ b/arch/sandbox/include/asm/u-boot-sandbox.h
@@ -87,6 +87,6 @@
 void sandbox_reset(void);
 
 /* Exit sandbox (quit U-Boot) */
-void sandbox_exit(void);
+void __noreturn sandbox_exit(void);
 
 #endif	/* _U_BOOT_SANDBOX_H_ */