staging: unisys: visorbus: variable adjustment should be a u64

This patch fixes the smatch error:

drivers/staging/unisys/visorbus/visorchipset.c:2217 visorchipset_ioctl()
warn: user controlled 'adjustment' cast to postive rl = 's64min-s64max'

This is because we read a s64 and pass it to a function as u64.

Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>