intel: decoder: fix starting dword of struct fields

intel: decoder: fix starting dword of struct fields

Struct fields might span several dwords, but iter_dword is incremented
up to the last dword of the current field before we print out the
struct's fields. We can't use iter_dword for computing the offset into
the pointer of data to decode.

v2: Fix displayed offset number (Ken)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>