i2c: qcom-geni: fix error return code in geni_i2c_gpi_xfer

Fix to return a negative error code from the gi2c->err instead of
0.

Fixes: d8703554

 ("i2c: qcom-geni: Add support for GPI DMA")
Signed-off-by: Wang Yufen <wangyufen@huawei.com>
Reviewed-by: Tommaso Merciai <tommaso.merciai@amarulasoluitons.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>