iwlwifi: simplify calibration collection

The calibration results all come in while we're
waiting for the calibration complete notification.
As a consequence, there's no need to install a
global RX handler for them, we can use the newly
extended notification wait framework for this and
make the code easier to follow.

It is now quite explicit that we are processing
the calibration results while waiting for the
complete notification, before this was implicit
and developers had to know this to understand why
we wait for the calibration complete notification
and what happens while we wait.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>