i965: Use ctx->Const.MaxLineWidth when clamping ctx->Line.Width.

i965: Use ctx->Const.MaxLineWidth when clamping ctx->Line.Width.

Rather than hardcoding platform values in every code path, just use the
maximum value we set.

Currently, ctx->Const.LineWidth == 5, which is smaller than the hardware
limit.  But applications shouldn't be using a value larger than we
support anyway.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>