i965/rbc: Clarify rational given for shader image resolves

i965/rbc: Clarify rational given for shader image resolves

Original commit added documentation explaining lossless compression
case:

commit 56f29911ec9da25c78fbd3d4945d499e65ca4b5a
Author: Topi Pohjolainen <topi.pohjolainen@intel.com>
Date:   Tue Feb 2 10:00:41 2016 +0200

    i965: Add a flag telling color resolve pass to ignore CCS_E

It, however, easily gives the impression that the sole purpose
of the intel_miptree_resolve_color() is to address lossless
compression. Original intention is to document the lack of
INTEL_MIPTREE_IGNORE_CCS_E flag given for the resolve call.

This patch fixes this along with a typo found spotted further
down.

Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>