staging: r8188eu: remove test in usbctrl_vendorreq()

staging: r8188eu: remove test in usbctrl_vendorreq()

Remove unnecessary test for "!io_buf" in usbctrl_vendorreq(). This test
is not necessary because io_buf has been assigned with the address of
a region of dynamically allocated memory (dvobj->usb_alloc_vendor_req_buf)
by rtw_init_intf_priv() in os_dep/usb_intf.c.

Co-developed-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Link: https://lore.kernel.org/r/20210924122705.3781-4-fmdefrancesco@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>