ACPI / debugger: remove some unneeded conditions

"count" is unsigned so checking for less than zero here causes a static
checker warning.  And really it's better to let the access_ok() check
fail if the user passes in a NULL "buf" pointer because -EFAULT is the
correct error code.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>