gapil/compiler/plugins/encoder: Fix MEC of state blocks
gapil/compiler/plugins/encoder: Fix MEC of state blocks

The type of the this pointer to state encoding was wrong - it was a pointer to the root of all states, when it should have been to the specific API state.
This resulted in gles MEC working fine (it's at the 0'th offset of the root state), but broke vulkan.

google/agi,google/gapid,Qining/gapid,google/gapid,Qining/gapid,google/agi,pmuetschard/gapid,Qining/gapid,Qining/gapid,google/agi,google/gapid,google/gapid,pmuetschard/gapid,Qining/gapid,google/gapid,google/gapid,google/gapid,pmuetschard/gapid,Qining/gapid,google/agi,google/agi,google/gapid,Qining/gapid,google/agi,pmuetschard/gapid,pmuetschard/gapid,google/agi,Qining/gapid,pmuetschard/gapid,pmuetschard/gapid,pmuetschard/gapid,google/agi