fix various issues

- code style
- variable initialize
- update comments


Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index 3948ea6..32a4f2a 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -1572,10 +1572,9 @@
                                             unsigned char **psk,
                                             size_t *psk_len )
 {
-
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     psa_key_attributes_t key_attributes = PSA_KEY_ATTRIBUTES_INIT;
-    psa_status_t status;
+    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
 
     *psk_len = 0;
     *psk = NULL;
@@ -1585,16 +1584,12 @@
 
     status = psa_get_key_attributes( ssl->handshake->psk_opaque, &key_attributes );
     if( status != PSA_SUCCESS )
-    {
         return( psa_ssl_status_to_mbedtls( status ) );
-    }
 
     *psk_len = PSA_BITS_TO_BYTES( psa_get_key_bits( &key_attributes ) );
     *psk = mbedtls_calloc( 1, *psk_len );
     if( *psk == NULL )
-    {
         return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
-    }
 
     status = psa_export_key( ssl->handshake->psk_opaque,
                              (uint8_t *)*psk, *psk_len, psk_len );