staging: rtl8712: fix use after free bugs

_Read/Write_MACREG callbacks are NULL so the read/write_macreg_hdl()
functions don't do anything except free the "pcmd" pointer. It
results in a use after free. Delete them.

Fixes: 2865d42c78a9 ("staging: r8712u: Add the new driver to the mainline kernel")
Cc: stable <[e-mail]>
Reported-by: Zheng Wang <[e-mail]>
Signed-off-by: Dan Carpenter <[e-mail]>
Link: https://lore.kernel.org/r/Yw4ASqkYcUhUfoY2@kili
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/rtl8712/rtl8712_cmd.c

···
 	kfree(pdrvcmd->pbuf);
 }
 
-static u8 read_macreg_hdl(struct _adapter *padapter, u8 *pbuf)
-{
-	void (*pcmd_callback)(struct _adapter *dev, struct cmd_obj	*pcmd);
-	struct cmd_obj *pcmd  = (struct cmd_obj *)pbuf;
-
-	/*  invoke cmd->callback function */
-	pcmd_callback = cmd_callback[pcmd->cmdcode].callback;
-	if (!pcmd_callback)
-		r8712_free_cmd_obj(pcmd);
-	else
-		pcmd_callback(padapter, pcmd);
-	return H2C_SUCCESS;
-}
-
-static u8 write_macreg_hdl(struct _adapter *padapter, u8 *pbuf)
-{
-	void (*pcmd_callback)(struct _adapter *dev, struct cmd_obj	*pcmd);
-	struct cmd_obj *pcmd  = (struct cmd_obj *)pbuf;
-
-	/*  invoke cmd->callback function */
-	pcmd_callback = cmd_callback[pcmd->cmdcode].callback;
-	if (!pcmd_callback)
-		r8712_free_cmd_obj(pcmd);
-	else
-		pcmd_callback(padapter, pcmd);
-	return H2C_SUCCESS;
-}
-
 static u8 read_bbreg_hdl(struct _adapter *padapter, u8 *pbuf)
 {
 	struct cmd_obj *pcmd  = (struct cmd_obj *)pbuf;
···
 	pcmd_r = NULL;
 
 	switch (pcmd->cmdcode) {
-	case GEN_CMD_CODE(_Read_MACREG):
-		read_macreg_hdl(padapter, (u8 *)pcmd);
-		pcmd_r = pcmd;
-		break;
-	case GEN_CMD_CODE(_Write_MACREG):
-		write_macreg_hdl(padapter, (u8 *)pcmd);
-		pcmd_r = pcmd;
-		break;
 	case GEN_CMD_CODE(_Read_BBREG):
 		read_bbreg_hdl(padapter, (u8 *)pcmd);
 		break;