media: ipu6: use PFN_UP() and sg_virt() for code simplicity

Use PFN_UP() and sg_virt() can be used to simplify the code.

Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>