This function is more useful if it takes just the min filter mode
instead of the entire sampler struct to read a single member.

Bug: b/167404532
Change-Id: Ie8c01c4095a615f06fe046fb175cdfb92fa54cbf
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2419111Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>