doxygen: fix parameter name typos and misused \p commands

\p is reserved for function parameters.
\c is used to describe other values and variables.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/include/mbedtls/dhm.h b/include/mbedtls/dhm.h
index 6ffe681..0232a71 100644
--- a/include/mbedtls/dhm.h
+++ b/include/mbedtls/dhm.h
@@ -325,7 +325,7 @@
  *                 initialized.
  *
  * \return         \c 0 on success.
- * \return         #MBEDTLS_ERR_DHM_BAD_INPUT_DATA if \p field is invalid.
+ * \return         #MBEDTLS_ERR_DHM_BAD_INPUT_DATA if \p param is invalid.
  * \return         An \c MBEDTLS_ERR_MPI_XXX error code if the copy fails.
  */
 int mbedtls_dhm_get_value(const mbedtls_dhm_context *ctx,