st/mesa: MAX_VARYING is the max supported number of patch varyings, not min
st/mesa: MAX_VARYING is the max supported number of patch varyings, not min

This fixes
GL45-CTS.tessellation_shader.tessellation_shader_tessellation.max_in_out_attributes
on nouveau. We only support 30 patch varyings (as 2 vec4 slots end up
being used for tess level settings), but were getting 32 exposed.

Signed-off-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>
Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>
Cc: "13.0 17.0" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler