Fix HFP AT command BIA failures

Running the PTE test case TC_AG_IIA_BV_01_I, a failure occurs due to
missing initialization of tBTA_AG_VAL.

Bug: 31325270
Test: PTS
Change-Id: I683eccd53d40e79ec03545166b18ffa1922f0fb2
diff --git a/bta/ag/bta_ag_cmd.c b/bta/ag/bta_ag_cmd.c
index 110b531..e3f7750 100644
--- a/bta/ag/bta_ag_cmd.c
+++ b/bta/ag/bta_ag_cmd.c
@@ -1113,6 +1113,7 @@
     APPL_TRACE_DEBUG("HFP AT cmd:%d arg_type:%d arg:%d arg:%s", cmd, arg_type,
                       int_arg, p_arg);
 
+    memset(&val, 0, sizeof(tBTA_AG_VAL));
     val.hdr.handle = bta_ag_scb_to_idx(p_scb);
     val.hdr.app_id = p_scb->app_id;
     val.hdr.status = BTA_AG_SUCCESS;