Use XPT_GET_ADVINFO for retrieving MMC params

[scottl]

Summary

Fix the accidental ABI breakage for CCBs and use the ADVINFO CCB
for retrieving the mmc_params structure.

[imp]

This looks good to me, modulo my one question...
I'll test it out shortly.

sys/cam/mmc/mmc_xpt.c

373 ↗

(On Diff #37822)

I assume the ioctl takes care of setting up the kernel buffer for this, then copying it out to user space?

[scottl]

sys/cam/mmc/mmc_xpt.c

373 ↗

(On Diff #37822)

I believe it's handled automatically in cam_periph_mapmem()

[kibab]

This change LGTM, I would like to know how this was discovered?

[scottl]

I came across it during some other clean-up work.