wifi: iwlwifi: pcie: fix RB status reading

wifi: iwlwifi: pcie: fix RB status reading

On newer hardware, a queue's RB status / write pointer
can be bigger than 4095 (0xFFF), so we cannot mask the
value by 0xFFF unconditionally. Since anyway that's
only necessary on older hardware, move the masking to
the helper function and apply it only for older HW.
This also moves the endian conversion in to handle it
more easily.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230830112059.7be2a3fff6f4.I94f11dee314a4f7c1941d2d223936b1fa8aa9ee4@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>