external/boringssl: bump revision.

This change bumps the BoringSSL revision to the current tip-of-tree.

Change-Id: I91d5bf467e16e8d86cb19a4de873985f524e5faa
diff --git a/src/crypto/bn/sqrt.c b/src/crypto/bn/sqrt.c
index 07041f9..e71a818 100644
--- a/src/crypto/bn/sqrt.c
+++ b/src/crypto/bn/sqrt.c
@@ -420,7 +420,7 @@
 
 end:
   if (err) {
-    if (ret != NULL && ret != in) {
+    if (ret != in) {
       BN_clear_free(ret);
     }
     ret = NULL;