iwlwifi: pcie: remove minor dead code

inta is checked to be zero in a IRQ_NONE branch so afterwards it
cannot be zero as it is never modified.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
[reword the patch title and fix comment]
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>