HID: hid-roccat-koneplus: potential NULL dereference

kmalloc() may fail, if so return -ENOMEM.
Also koneplus_init_koneplus_device_struct() should check return code
of koneplus_get_startup_profile() and propagate its return code.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>