wlcore: spi: use platform_device_unregister in wl1271_remove()
platform_device_unregister() only calls platform_device_del() and
platform_device_put(), thus use platform_device_unregister() to
simplify the code.
Also the documents in platform.c shows that platform_device_del
and platform_device_put must _only_ be externally called in error
cases. All other usage is a bug.
dpatch engine is used to auto generate this patch.
(https://github.com/weiyj/dpatch)