glsl: Fix assertion checking types of constant bitshift expressions.
glsl: Fix assertion checking types of constant bitshift expressions.

Bitshifts are one of the rare places that GLSL allows mixed base types
without an implicit conversion occurring.

Reviewed-by: Chad Versace <c34c009102e60d77975598e1f414f8a701c22d0b@chad-versace.us>
Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

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