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>

drivers/staging/unisys/visorbus/visorchipset.c

@@ -2248,7 +2248,7 @@ static inline int issue_vmcall_update_physical_time(u64 adjustment)
 static long visorchipset_ioctl(struct file *file, unsigned int cmd,
 			       unsigned long arg)
 {
-	s64 adjustment;
+	u64 adjustment;
 	s64 vrtc_offset;
 
 	switch (cmd) {