vbo: fix incorrect switch statement in init_mat_currval()
vbo: fix incorrect switch statement in init_mat_currval()

The variable 'i' is a value in [0, MAT_ATTRIB_MAX-1] so subtracting
VERT_ATTRIB_GENERIC0 gave a bogus value and we executed the default
switch clause for all loop iterations.

This doesn't fix any known issues but was clearly incorrect.

Cc: mesa-stable@lists.freedesktop.org

Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler