draw: fix PIPE_MAX_SAMPLER/PIPE_MAX_SHADER_SAMPLER_VIEWS issues

draw: fix PIPE_MAX_SAMPLER/PIPE_MAX_SHADER_SAMPLER_VIEWS issues

pstipple/aaline stages used PIPE_MAX_SAMPLER instead of
PIPE_MAX_SHADER_SAMPLER_VIEWS when dealing with sampler views.
Now these stages can't actually handle sampler_unit != texture_unit anyway
(they cannot work with d3d10 shaders at all due to using tex not sample
opcodes as "mixed mode" shaders are impossible) but this leads to crashes if
a driver just installs these stages and then more than PIPE_MAX_SAMPLER views
are set even if the stages aren't even used.

Reviewed-by: Zack Rusin <zackr@vmware.com>