sandbox: Correct error handling in state_read_file()

This function should return a useful error for U-Boot, rather than -1.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/arch/sandbox/cpu/state.c b/arch/sandbox/cpu/state.c
index 033958c..cae731c 100644
--- a/arch/sandbox/cpu/state.c
+++ b/arch/sandbox/cpu/state.c
@@ -51,7 +51,7 @@
 	ret = os_get_filesize(fname, &size);
 	if (ret < 0) {
 		printf("Cannot find sandbox state file '%s'\n", fname);
-		return ret;
+		return -ENOENT;
 	}
 	state->state_fdt = os_malloc(size);
 	if (!state->state_fdt) {