ref(image): use named constant for TGA mode mask value
ref(image): use named constant for TGA mode mask value

zenmumbler/stardazed-tx,stardazed/stardazed,stardazed/stardazed-tx,zenmumbler/libzm,stardazed/stardazed-tx,zenmumbler/libzm,zenmumbler/stardazed-tx,stardazed/stardazed-tx,zenmumbler/stardazed-tx,stardazed/stardazed,zenmumbler/libzm,zenmumbler/libzm,zenmumbler/stardazed-tx