staging: rtl8723bs: os_dep: remove rtw_spt_band_free()

Now that rtw_spt_band_free() is only a direct wrapper of kfree, we can
remove it and just use kfree().

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Link: https://lore.kernel.org/r/20200428133115.28072-1-yanaijie@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>