mesa/tex: storing with proper src-stride

During storing sub-image of compressed texture a wrong stride of src may be computed. Catched when were trying to replay dota2-apitrace (crash).

CI: https://mesa-ci.01.org/global_logic/builds/192/group/63a9f0ea7bb98050796b649e85481845

CC: Chris Forbes chrisf@ijw.co.nz CC: Ian Romanick ian.d.romanick@intel.com Fixes: be30766f (mesa: Compute proper strides for compressed texture pixel storage) Signed-off-by: Sergii Romantsov sergii.romantsov@globallogic.com