radeon_replay/aruba_dp_aux: Add parentheses around bitwise shift

Fix the register write in aux_channel_fifo_write_start() to include
parentheses around "data << 8". There were no problems associated
with this line, but it makes the statement symmetrical wrt to also
setting of bit 31.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
radeon_replay/aruba_dp_aux: Do not set default for 'reply' field

Don't set the 'reply' field to 0xff if we get an error from
do_aux_tran(). An error means we haven't received a reply, and we
shouldn't use that field anyway on errors.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
radeon_replay/aruba_dp_aux: Move retry loop to separate function

Move the retry loop out of radeon_process_aux_ch_wrapper(). This
function is designed to plug into linux, but linux already has a retry
loop, and expects us to only try the transaction once.

For our internal purposes, call the wrapper which handles the retries.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>