i965: call intel_prepare_render always when reading pixels

i965: call intel_prepare_render always when reading pixels

Currently we do this only in the fallback code (when tiled memcpy
version failed) but it needs to be done always so that we have
correct read and write buffer in place. No regressions seen in CI.

Fixes:
	dEQP-EGL.functional.buffer_age.*

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98330
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chad Versace <chadversary@chromium.org>