iwlwifi: yoyo: don't print failure if debug firmware is missing

iwlwifi: yoyo: don't print failure if debug firmware is missing

Missing this firmware is not fatal, my wifi card still works. Even more,
I couldn't find any documentation what it is or where to get it. So, I
don't think the users should be notified if it is missing. If you browse
the net, you see the message is present is in quite some logs. Better
remove it.

Signed-off-by: Wolfram Sang <wsa@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200625165210.14904-1-wsa@kernel.org