mhi: dev: satellite: do not assert for unknown device

Satellite base driver can receive a message such as the
acknowledgment of SYS_ERROR command from clients after it has
timed out and proceeded with clean-up. If that ACK or any other
message comes later on and MHI host is yet to probe the
satellite driver after an SSR, those can be safely ignored.

Change-Id: Id3132506fa902c0513432b760926767d4f100c4a
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>