Remove duplicate '+' in comparison string

Signed-off-by: Agathiyan Bragadeesh <agathiyan.bragadeesh2@arm.com>
diff --git a/library/x509_create.c b/library/x509_create.c
index a666e2d..4c52611 100644
--- a/library/x509_create.c
+++ b/library/x509_create.c
@@ -197,7 +197,7 @@
                 hexpair = 1;
                 *(d++) = n;
                 c++;
-            } else if (c == end || !strchr(" ,=+<>#;\"\\+", *c)) {
+            } else if (c == end || !strchr(" ,=+<>#;\"\\", *c)) {
                 return MBEDTLS_ERR_X509_INVALID_NAME;
             }
         }