Fx DH_set0_pqg.

Typo.

Change-Id: Iab3e04339bb868fd6d247c6696f33f5b7150408d
Reviewed-on: https://boringssl-review.googlesource.com/21184
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Martin Kreichgauer <martinkr@google.com>
Reviewed-by: Martin Kreichgauer <martinkr@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/crypto/dh/dh.c b/crypto/dh/dh.c
index 04e245e..7b7b833 100644
--- a/crypto/dh/dh.c
+++ b/crypto/dh/dh.c
@@ -167,7 +167,7 @@
     dh->q = q;
   }
 
-  if (g == NULL) {
+  if (g != NULL) {
     BN_free(dh->g);
     dh->g = g;
   }