drm/radeon/kms/atom: fix gpio i2c table overrun (v2)

The GPIO_I2C_INFO table does not always have
ATOM_MAX_SUPPORTED_DEVICE entries. Limit
the number of indices to the size of the
table.

Should fix Novell bug 589022.

v2: fix typo

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: Stable <stable@kernel.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>