mwifiex: don't complain about 'unknown event id: 0x63'

Marvell folks tell me this is a debugging event that the driver doesn't
need to handle, but on 8997 w/ firmware 16.68.1.p97, I see several of
these sorts of messages at (for instance) boot time:

[   13.825848] mwifiex_pcie 0000:01:00.0: event: unknown event id: 0x63
[   14.838561] mwifiex_pcie 0000:01:00.0: event: unknown event id: 0x63
[   14.850397] mwifiex_pcie 0000:01:00.0: event: unknown event id: 0x63
[   32.529923] mwifiex_pcie 0000:01:00.0: event: unknown event id: 0x63

Let's handle this "event" with a much lower verbosity.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>