fw-update: Notify UpdateManager on response decode failure

DeviceUpdater response handlers follow a common pattern: if
response is null, the decoder fails, or the completion code is
non-zero, the device cannot complete the update and the handler
logs an error and returns. The null-response and completion-code
paths correctly notify UpdateManager via updateDeviceCompletion(),
but the decode-failure path silently returns, leaving the software
object in InProgress state indefinitely.

Add updateDeviceCompletion(eid, false) calls to four decode
failure paths so the state machine correctly transitions to
failure:
  - requestUpdate()       (decode_request_update_resp)
  - passCompTable()       (decode_pass_component_table_resp)
  - updateComponent()     (decode_update_component_resp)
  - activateFirmware()    (decode_activate_firmware_resp)

cancelUpdateComponent() is intentionally left unchanged because
it is the cleanup path for an already-failed update.

Reported-by: Vishnunithyasoundhar S (on Gerrit 87785 PS8)
Tested: E2E on Renode evb-ast2600-renode with malformed
UpdateComponent response injection — pldmd correctly logs
decode failure and calls updateDeviceCompletion(eid, false).
Robot test "Should Handle Malformed Update Component Response"
passes. clang-format clean, Docker CI builds cleanly.

Change-Id: Ie04b385abcb86f5fb815cfddb6ec95bca053a19f
Signed-off-by: Gary Beihl <garybeihl@microsoft.com>