net: disable MBEDTLS in SPL

Building SPL fails with MBEDTLS enabled.
Currently we don't need it there.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
diff --git a/lib/sha1.c b/lib/sha1.c
index a9d6497..be502c6 100644
--- a/lib/sha1.c
+++ b/lib/sha1.c
@@ -312,14 +312,16 @@
 		  unsigned char *output, unsigned int chunk_sz)
 {
 	sha1_context ctx;
-#if defined(CONFIG_HW_WATCHDOG) || defined(CONFIG_WATCHDOG)
+#if !defined(USE_HOSTCC) && \
+    (defined(CONFIG_HW_WATCHDOG) || defined(CONFIG_WATCHDOG))
 	const unsigned char *end, *curr;
 	int chunk;
 #endif
 
 	sha1_starts (&ctx);
 
-#if defined(CONFIG_HW_WATCHDOG) || defined(CONFIG_WATCHDOG)
+#if !defined(USE_HOSTCC) && \
+    (defined(CONFIG_HW_WATCHDOG) || defined(CONFIG_WATCHDOG))
 	curr = input;
 	end = input + ilen;
 	while (curr < end) {