native_gfx_vivfb: use fbGetDisplay(NULL) instead of fbGetDisplayByIndex(0)
native_gfx_vivfb: use fbGetDisplay(NULL) instead of fbGetDisplayByIndex(0)

This is for better portability.

Signed-off-by: Julien Olivain <7fdfe229fce69a4d7f38653f3755ccbae5703f88@cotds.org>

jolivain/glslsandbox-player,jolivain/glslsandbox-player,jolivain/glslsandbox-player,jolivain/glslsandbox-player