pmic: qcom: dont use dev_read_addr to get USID

Linux DTs stuff a value indicating if the USID is a USID or a GSID in the
reg property, the Linux SPMI driver then reads the two address cells
separately. U-boot's dev_read_addr() doesn't know how to handle this, so
use ofnode_read_u32_index() to get just the USID.

The Qcom pmic driver doesn't have support for GSID handling, so just
ignore the second value for now.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Tested-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>