usb: isp1760: Fix meaningless check in isp1763_run()

Remove attribution to retval before check, which make it completely
meaningless, and does't check what it was supposed: the return
value of the timed function to set up configuration flag.

Fixes: 60d789f3

 ("usb: isp1760: add support for isp1763")
Tested-by: Rui Miguel Silva <rui.silva@linaro.org>
Reviewed-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
Link: https://lore.kernel.org/r/20210611014055.68551-1-tongtiangen@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>