Compilation fails with old mbedtls (2.4.2)

Fix:

diff --git a/src/eap.c b/src/eap.c
index efffa4e..70604d9 100644
--- a/src/eap.c
+++ b/src/eap.c
@@ -305,7 +305,7 @@ static int process_eap_response_identity(struct eapsrp_ctx *ctx, size_t len, uin
                        memset(&outpkt[offset], 0, 2);
                        offset += 2;
                } else {
-                       struct mbedtls_mpi tmp;
+                       mbedtls_mpi tmp;
                        mbedtls_mpi_init(&tmp);
                        mbedtls_mpi_read_string(&tmp, 16, ascii_g);
                        tmp_swap = (uint16_t *)&outpkt[offset];