Remove superfluous sizeof(unsigned char)

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/library/oid.c b/library/oid.c
index 3b5b31a..1031990 100644
--- a/library/oid.c
+++ b/library/oid.c
@@ -1008,7 +1008,7 @@
         encoded_len += num_bytes;
     }
 
-    oid->p = mbedtls_calloc(encoded_len, sizeof(unsigned char));
+    oid->p = mbedtls_calloc(encoded_len, 1);
     if (oid->p == NULL) {
         return MBEDTLS_ERR_ASN1_ALLOC_FAILED;
     }