cxl: remove redundant increment of hwirq

hwirq has not been initialized, however it is being incremented
and also not being referenced in a loop.  This error was detected with
cppcheck:

[drivers/misc/cxl/irq.c:439]: (error) Uninitialized variable: hwirq

Commit 80fa93fc ("cxl: Name interrupts in /proc/interrupt")
introduced this error.

This is a simple fix that removes the redundant increment.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-By: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>