drm/radeon/atom: fix bus probes when hw_i2c is set (v2)

When probing the bus, we need to set the byte count
to 0 rather than 1.

v2: Don't count the first byte.

bug:
https://bugzilla.kernel.org/show_bug.cgi?id=66241



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org