gallivm: fix bogus argument order to lp_build_sample_mipmap function

gallivm: fix bogus argument order to lp_build_sample_mipmap function

Screwed up since 0753b135f6e83b171d8a1b08aea967374f3542bc.

(Only an issue with different min/mag filters, and then only in some cases,
which is probably why it went unnoticed for quite a while.
The effect should have simply been nearest mip filter instead of linear, iff
min was nearest, mag was linear, and all pixels hit the mignifying path.)

Fixes a bunch of dEQP failures.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Cc: "11.1 11.2" <mesa-stable@lists.freedesktop.org>