Fix additional misspellings found by codespell

Remaining hits seem to be hex data, certificates,
and other miscellaneous exceptions.
List generated by running codespell -w -L 
keypair,Keypair,KeyPair,keyPair,ciph,nd

Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 06ee46b..9de9d6d 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -982,7 +982,7 @@
 #endif /* MBEDTLS_RSA_C */
         default:
             MBEDTLS_SSL_DEBUG_MSG( 1,
-                                   ( "unkown signature type : %u", sig ) );
+                                   ( "unknown signature type : %u", sig ) );
             break;
     }
     return( -1 );