staging: r8188eu: fix a potential memory leak in rtw_init_cmd_priv()

staging: r8188eu: 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 not be properly
released. Besides, considering there are only two error paths and the
first one can directly return, we do not need to implicitly jump to the
`exit` tag to execute the error handling code.

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.

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Signed-off-by: Xiaoke Wang <xkernel.wang@foxmail.com>
Link: https://lore.kernel.org/r/tencent_1B6AAE10471D4556788892F8FF3E4812F306@qq.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>