Fix some typo for include folder

Signed-off-by: Wenxing Hou <wenxing.hou@intel.com>
diff --git a/include/mbedtls/ecdh.h b/include/mbedtls/ecdh.h
index a0909d6..a6a5069 100644
--- a/include/mbedtls/ecdh.h
+++ b/include/mbedtls/ecdh.h
@@ -325,7 +325,7 @@
  * \brief           This function sets up an ECDH context from an EC key.
  *
  *                  It is used by clients and servers in place of the
- *                  ServerKeyEchange for static ECDH, and imports ECDH
+ *                  ServerKeyExchange for static ECDH, and imports ECDH
  *                  parameters from the EC key information of a certificate.
  *
  * \see             ecp.h