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/ecp.h b/include/mbedtls/ecp.h
index 5402e74..d56069e 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -1081,7 +1081,7 @@
  *
  *                  It only checks that the point is non-zero, has
  *                  valid coordinates and lies on the curve. It does not verify
- *                  that it is indeed a multiple of \p G. This additional
+ *                  that it is indeed a multiple of \c G. This additional
  *                  check is computationally more expensive, is not required
  *                  by standards, and should not be necessary if the group
  *                  used has a small cofactor. In particular, it is useless for
@@ -1106,7 +1106,7 @@
                              const mbedtls_ecp_point *pt);
 
 /**
- * \brief           This function checks that an \p mbedtls_mpi is a
+ * \brief           This function checks that an \c mbedtls_mpi is a
  *                  valid private key for this curve.
  *
  * \note            This function uses bare components rather than an