genirq/ipi: Fix NULL pointer deref in irq_data_get_affinity_mask()

In the Linux kernel, the following vulnerability has been resolved:

genirq/ipi: Fix NULL pointer deref in irq_data_get_affinity_mask()

If ipi_send_{mask|single}() is called with an invalid interrupt number, all
the local variables there will be NULL. ipi_send_verify() which is invoked
from these functions does verify its 'data' parameter, resulting in a
kernel oops in irq_data_get_affinity_mask() as the passed NULL pointer gets
dereferenced.

Add a missing NULL pointer check in ipi_send_verify()...

Found by Linux Verification Center (linuxtesting.org) with the SVACE static
analysis tool.