staging: rtl8723bs: Fix a resource leak in sd_int_dpc

The "c2h_evt" variable is not freed when function call
"c2h_evt_read_88xx" failed

Fixes: 554c0a3a

 ("staging: Add rtl8723bs sdio wifi driver")
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Xiangyang Zhang <xyz.sun.ok@gmail.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210628152239.5475-1-xyz.sun.ok@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>