sysreset: Fix unsupported request return values

The description of the sysreset request method in <sysreset.h> says that
the return value should be -EPROTONOSUPPORT if the requested reset type
is not supported by this device.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/sysreset/sysreset_sandbox.c b/drivers/sysreset/sysreset_sandbox.c
index f485a13..c12eda8 100644
--- a/drivers/sysreset/sysreset_sandbox.c
+++ b/drivers/sysreset/sysreset_sandbox.c
@@ -21,7 +21,7 @@
 		state->last_sysreset = type;
 		break;
 	default:
-		return -ENOSYS;
+		return -EPROTONOSUPPORT;
 	}
 	if (!state->sysreset_allowed[type])
 		return -EACCES;
@@ -70,7 +70,7 @@
 			return -EACCES;
 		sandbox_exit();
 	default:
-		return -ENOSYS;
+		return -EPROTONOSUPPORT;
 	}
 	if (!state->sysreset_allowed[type])
 		return -EACCES;