svga: store shared_mem_size in svga_compute_shader instead of svga_context
When new context was created, shared_mem_size was getting overwritten. This fixes glretrace failure seen with manhattan, aztec and BASS2_intro apitraces
Fixes: 247c61f2 ('svga: Add support for compute shader, shader buffers and image views')
Tested with glretrace, piglit
Reviewed-by: Charmaine Lee charmainel@vmware.com (cherry picked from commit dd6793ec9218782b1b716a87582d7219bae4e75f)