has: Fix false encryption success

The event alone does not mean the encryption was successfully enabled.

Bug: 243648269
Fixes: 243648269
Tag: #feature
Test: atest bluetooth_has_test --no-bazel-mode
Change-Id: I2c5cc8d153f293860268378fb163d6e06f28ba1e
Merged-In: I2c5cc8d153f293860268378fb163d6e06f28ba1e
(cherry picked from commit af24d553)