Shut up a few clang-analyze warnings about use of uninitialized variables

The functions are all safe, Clang just isn't clever enough to realise
it.
diff --git a/library/pkcs12.c b/library/pkcs12.c
index 7023b9d..c603a13 100644
--- a/library/pkcs12.c
+++ b/library/pkcs12.c
@@ -93,7 +93,7 @@
                                      unsigned char *key, size_t keylen,
                                      unsigned char *iv,  size_t ivlen )
 {
-    int ret, iterations;
+    int ret, iterations = 0;
     mbedtls_asn1_buf salt;
     size_t i;
     unsigned char unipwd[PKCS12_MAX_PWDLEN * 2 + 2];