gapii: Fix type for ANativeWindowBuffer::layer_count.
gapii: Fix type for ANativeWindowBuffer::layer_count.

I have no excuses for why I got this wrong first time.

Fixes: #1508

google/gapid,google/gapid,baldwinn860/gapid,Qining/gapid,Qining/gapid,pmuetschard/gapid,baldwinn860/gapid,pmuetschard/gapid,Qining/gapid,google/gapid,baldwinn860/gapid,Qining/gapid,google/gapid,Qining/gapid,google/gapid,baldwinn860/gapid,google/agi,pmuetschard/gapid,pmuetschard/gapid,baldwinn860/gapid,Qining/gapid,google/agi,google/agi,pmuetschard/gapid,google/gapid,google/gapid,google/agi,google/agi,Qining/gapid,baldwinn860/gapid,pmuetschard/gapid,google/agi,google/agi,Qining/gapid,pmuetschard/gapid,google/gapid,pmuetschard/gapid,baldwinn860/gapid,baldwinn860/gapid,google/agi