Fix maybe-uninitialized warning

GCC 4.8 warns that some variables may be used without having been
initialized. They aren't, but determining that takes nontrivial
analysis, so initialize them at the point of definition.

Author: gilles-peskine-arm

programs/psa/key_ladder_demo.c

@@ -393,7 +393,7 @@ static psa_status_t wrap_data( const char *input_file_name,
     FILE *output_file = NULL;
     long input_position;
     size_t input_size;
-    size_t buffer_size;
+    size_t buffer_size = 0;
     unsigned char *buffer = NULL;
     size_t ciphertext_size;
     wrapped_data_header_t header;
@@ -469,7 +469,7 @@ static psa_status_t unwrap_data( const char *input_file_name,
     FILE *input_file = NULL;
     FILE *output_file = NULL;
     unsigned char *buffer = NULL;
-    size_t ciphertext_size;
+    size_t ciphertext_size = 0;
     size_t plaintext_size;
     wrapped_data_header_t header;
     unsigned char extra_byte;