panfrost/midgard: Print the actual source register for store operations

panfrost/midgard: Print the actual source register for store operations

Store operation use r26/r27 but have a word->reg set to 0 or 1 (base is
r26). Let's take this base offset into account in
print_load_store_instr().

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3482>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3482>