USB: usblp: return error when setting unsupported protocol

USB: usblp: return error when setting unsupported protocol

Fix the regression introduced by commit d8c6edfa3f4e ("USB:
usblp: don't call usb_set_interface if there's a single alt"),
which causes that unsupported protocols can also be set via
ioctl when the num_altsetting of the device is 1.

Move the check for protocol support to the earlier stage.

Fixes: d8c6edfa3f4e ("USB: usblp: don't call usb_set_interface if there's a single alt")
Cc: stable <stable@kernel.org>
Signed-off-by: Jun Yan <jerrysteve1101@gmail.com>
Link: https://lore.kernel.org/r/20241212143852.671889-1-jerrysteve1101@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>