staging: gpib: Fix inadvertent negative shift

staging: gpib: Fix inadvertent negative shift

During the initial checkpatch cleanup, when removing blanks
after open parentheses, a minus sign in the argument of a shift
operation was deleted by mistake. This transformed a pre-decrement
operation into a negation.

The result of a negative shift is undefined and a warning was
signalled by sparse.

Restore the pre-decrement operation.

Fixes: 6c52d5e3cde2 ("staging: gpib: Add common include files for GPIB drivers")
Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Link: https://lore.kernel.org/r/20250116110014.15577-1-dpenkler@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>