staging: gpib: Fix faulty workaround for assignment in if

This was detected by Coverity.

Add the missing assignment in the else branch of the if

Reported-by: Kees Bakker <kees@ijzerbout.nl>
Fixes: fce79512 ("staging: gpib: Add LPVO DIY USB GPIB driver")
Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Link: https://lore.kernel.org/r/20241204145713.11889-5-dpenkler@gmail.com


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