st/nine: Fix centroid flag
st/nine: Fix centroid flag

sem.reg.mod & NINED3DSPDM_CENTROID is worth 4 when
centroid is requested, whereas
TGSI_INTERPOLATE_LOC_CENTROID is worth 1.

Signed-off-by: Axel Davy <2b6ef604b998fb81662f85c329e4fc020eae8e5d@ens.fr>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler