i8k: Fix non-SMP operation

i8k: Fix non-SMP operation

commit 6d827fbcc370ca259a2905309f64161ab7b10596 upstream.

Commit f36fdb9f0266 (i8k: Force SMM to run on CPU 0) adds support
for multi-core CPUs to the driver. Unfortunately, that causes it
to fail loading if compiled without SMP support, at least on
32 bit kernels. Kernel log shows "i8k: unable to get SMM Dell
signature", and function i8k_smm is found to return -EINVAL.

Testing revealed that the culprit is the missing return value check
of set_cpus_allowed_ptr.

Fixes: f36fdb9f0266 (i8k: Force SMM to run on CPU 0)
Reported-by: Jim Bos <jim876@xs4all.nl>
Tested-by: Jim Bos <jim876@xs4all.nl>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Cc: Andreas Mohr <andi@lisas.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>