qcacld-3.0: Unregister CSR scan request handler when csr_stop

Register CSR scan requester when csr_start(), but didn't unregister it
when csr_stop(). It might run out scan requester buffer.

Change-Id: I95472027c927ae0c0bc1869338cffad6bbacf0ff
CRs-Fixed: 2222492

core/sme/src/csr/csr_api_roam.c

@@ -1172,6 +1172,7 @@ QDF_STATUS csr_stop(tpAniSirGlobal pMac, tHalStopType stopType)
 		csr_roam_substate_change(pMac, eCSR_ROAM_SUBSTATE_NONE,
 					 sessionId);
 	}
+	ucfg_scan_unregister_requester(pMac->psoc, pMac->scan.requester_id);
 
 	return QDF_STATUS_SUCCESS;
 }