spmi: Include OF based modalias in device uevent

Include the OF-based modalias in the uevent sent when registering SPMI
devices, so that user space has a chance to autoload the kernel module
for the device.

Tested-by: Rob Clark <robdclark@gmail.com>
Reported-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>