ocxl: Fix potential bad errno on irq allocation

ocxl: Fix potential bad errno on irq allocation

BugLink: http://bugs.launchpad.net/bugs/1755161
Fix some issues found by a static checker:

When allocating an AFU interrupt, if the driver cannot copy the output
parameters to userland, the errno value was not set to EFAULT

Remove a (now) useless cast.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from commit 423688abd9ab654044bddd82eb5983189eb9630d)
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>