glsl: simplify buffer block resource limit checking

glsl: simplify buffer block resource limit checking

This changes the code to use the buffer counts stored for each stage
rather than counting from scratch. It also moves the checks outside
of the for loop which means we now just get a single link error
message if we go over the max rather than X error messages where X
is the number we have exceeded the max by.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>