Strict C99: don't use a signed* when an unsigned* is expected

It works in practice on almost every platform, given that we're only
using the wrong type in cases where the value is guaranteed to stay
within the value bits of a signed int. But even in this case it may or
may not be strictly conforming. Anyway `gcc -std=c99 -pedantic`
rejects it.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

programs/aes/crypt_and_hash.c

@@ -85,7 +85,8 @@ int main( void )
 
 int main( int argc, char *argv[] )
 {
-    int ret = 1, i, n;
+    int ret = 1, i;
+    unsigned n;
     int exit_code = MBEDTLS_EXIT_FAILURE;
     int mode;
     size_t keylen, ilen, olen;

programs/pkey/pk_decrypt.c

@@ -64,7 +64,8 @@ int main( void )
 int main( int argc, char *argv[] )
 {
     FILE *f;
-    int ret = 1, c;
+    int ret = 1;
+    unsigned c;
     int exit_code = MBEDTLS_EXIT_FAILURE;
     size_t i, olen = 0;
     mbedtls_pk_context pk;

programs/pkey/rsa_decrypt.c

@@ -65,7 +65,7 @@ int main( int argc, char *argv[] )
     FILE *f;
     int ret = 1;
     int exit_code = MBEDTLS_EXIT_FAILURE;
-    int c;
+    unsigned c;
     size_t i;
     mbedtls_rsa_context rsa;
     mbedtls_mpi N, P, Q, D, E, DP, DQ, QP;

programs/pkey/rsa_verify.c

@@ -59,7 +59,8 @@ int main( void )
 int main( int argc, char *argv[] )
 {
     FILE *f;
-    int ret = 1, c;
+    int ret = 1;
+    unsigned c;
     int exit_code = MBEDTLS_EXIT_FAILURE;
     size_t i;
     mbedtls_rsa_context rsa;