iwlwifi: pcie: use don't disable interrupt when irq_lock is taken

Since we don't take this lock in the primary interrupt
handler, there is no pointin disabling the interrupt
in the critical section protected by trans_pcie->irq_lock.

Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>