drivers/base/cpu: remove redundant assignment of variable retval

The variable retval is being initialized with a value that is never read
and it is being updated later with a new value.  Clean this up by
initializing retval to -ENOMEM and remove the assignment to retval
on the !dev failure path.

Kudos to Rafael for the improved fix suggestion.

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210218202837.516231-1-colin.king@canonical.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>