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>

arch/sandbox/cpu/state.c

@@ -51,7 +51,7 @@ static int state_read_file(struct sandbox_state *state, const char *fname)
 	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) {