llvmpipe: Fix variable name.

llvmpipe: Fix variable name.

Fix warning reported by Coverity Scan.

Unused value (UNUSED_VALUE)
assigned_value: Assigning value from res->nr_samples to
jit_tex->sample_stride here, but that stored value is overwritten before
it can be used.

Fixes: 2e5cddacf7fb ("llvmpipe: add num_samples/sample_stride support to jit textures")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3022
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5179>