meta: Make _mesa_meta_setup_sampler static

meta: Make _mesa_meta_setup_sampler static

   text     data     bss      dec    hex  filename
12244854 1344936 1290748 14880538 e30f1a  before/lib64/dri/i965_dri.so
12244406 1344936 1290748 14880090 e30d5a  after/lib64/dri/i965_dri.so

v2: Put static on the function definition too.  Suggested by Paulo.

v3: Reformat prototype.  Suggested by Jason.

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com> [v2]
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/856>