usb: usbtmc: Fix erroneous generic_read ioctl return

wait_event_interruptible_timeout returns a long
The return value was being assigned to an int causing an integer overflow
when the remaining jiffies > INT_MAX which resulted in random error
returns.

Use a long return value, converting to the int ioctl return only on error.

Fixes: bb99794a ("usb: usbtmc: Add ioctl for vendor specific read")
Cc: stable@vger.kernel.org
Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Link: https://lore.kernel.org/r/20250502070941.31819-4-dpenkler@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>