Reenable bn_div fuzzer.

It looks like the bn_div fuzzer was inadvertently removed from
fuzz/'s CMakeLists during an earlier refactor [1]. This change
adds it back.

[1]: https://boringssl-review.googlesource.com/c/boringssl/+/31324/

Change-Id: I8bb4b224eedff60cc5cd6df7fa39d9c39d499a56
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/38424
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

fuzz/CMakeLists.txt

diff --git a/fuzz/CMakeLists.txt b/fuzz/CMakeLists.txt
index ac0703f..98a959a 100644
--- a/fuzz/CMakeLists.txt
+++ b/fuzz/CMakeLists.txt
@@ -16,6 +16,7 @@
 
 fuzzer(arm_cpuinfo)
 fuzzer(bn_mod_exp)
+fuzzer(bn_div)
 fuzzer(privkey)
 fuzzer(cert)
 fuzzer(spki)