i965: Don't allocate uniform space for samplers

i965: Don't allocate uniform space for samplers

Samplers are encoded into the instruction word, so there's no need to
make space in the uniform file.

Previously matrix_columns and vector_elements were set to 0, making this
else case a no-op. Commit 75a31a20af26 changed that, causing malloc
corruption in thousands of tests on i965.

Fixes: 75a31a20af26 ("glsl: set vector_elements to 1 for samplers")
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100871