iwiwifi: fix bad monitor buffer register addresses

The monitor buffer register address is wrong.
Set the right address

Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Fixes: c2d20201 ("iwlwifi: pcie: add firmware monitor capabilities")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>