Fix IAR control bypasses initialisation warning

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/sha256.c b/library/sha256.c
index 5375255..223badf 100644
--- a/library/sha256.c
+++ b/library/sha256.c
@@ -681,6 +681,7 @@
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     uint32_t used;
     uint32_t high, low;
+    int truncated = 0;
 
     /*
      * Add padding: 0x80 then 0x00 until 8 bytes remain for the length
@@ -728,7 +729,6 @@
     MBEDTLS_PUT_UINT32_BE(ctx->state[5], output, 20);
     MBEDTLS_PUT_UINT32_BE(ctx->state[6], output, 24);
 
-    int truncated = 0;
 #if defined(MBEDTLS_SHA224_C)
     truncated = ctx->is224;
 #endif