Correct SPL uses of SIFIVE_OTP

This converts 2 usages of this option to the non-SPL form, since there is
no SPL_SIFIVE_OTP defined in Kconfig

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/sifive/unleashed/unleashed.c b/board/sifive/unleashed/unleashed.c
index f8aad86..b6ab06a 100644
--- a/board/sifive/unleashed/unleashed.c
+++ b/board/sifive/unleashed/unleashed.c
@@ -27,7 +27,7 @@
 
 #ifdef CONFIG_MISC_INIT_R
 
-#if CONFIG_IS_ENABLED(SIFIVE_OTP)
+#if IS_ENABLED(CONFIG_SIFIVE_OTP)
 static u32 otp_read_serialnum(struct udevice *dev)
 {
 	int ret;
@@ -53,7 +53,7 @@
 {
 	u32 serial = ERROR_READING_SERIAL_NUMBER;
 
-#if CONFIG_IS_ENABLED(SIFIVE_OTP)
+#if IS_ENABLED(CONFIG_SIFIVE_OTP)
 	struct udevice *dev;
 	int ret;