staging: rtl8723bs: fix a potential memory leak in rtw_init_cmd_priv()

In the Linux kernel, the following vulnerability has been resolved: staging: rtl8723bs: fix a potential memory leak in rtw_init_cmd_priv() In rtw_init_cmd_priv(), if `pcmdpriv->rsp_allocated_buf` is allocated in failure, then `pcmdpriv->cmd_allocated_buf` will be not properly released. Besides, considering there are only two error paths and the first one can directly return, so we do not need implicitly jump to the `exit` tag to execute the error handler. So this patch added `kfree(pcmdpriv->cmd_allocated_buf);` on the error path to release the resource and simplified the return logic of rtw_init_cmd_priv(). As there is no proper device to test with, no runtime testing was performed.