iwlwifi: pcie: add missing calls to synchronize_irq()

In a few places, we were disabling interrupts but didn't
make sure that the interrupt handler has finished running.
Add calls to synchronize_irq() to ensure we finish handling
the interrupts before we free resources or other things that
could lead to a crash if the interrupt were to be handled
later.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>