Sanity check BIOS EDD CHS numbers before using them.

[delphij]

Summary

In r337271, we limited the sector number to the lower of calculated
number and CHS based number. However, on some systems, BIOS would
report 0 in CHS fields, making the system to think there is 0 sectors.

Add a check before comparing the calculated total with bd_sectors.

Test Plan

boot

[dhw]

The above change allowed a kernel to load on my laptop[[ https://wiki.freebsd.org/Laptops/Dell_Precision_M4800?highlight=(\bCategoryLaptop\b)| Dell Precision M4800 ]] after updating from r337232 -> r337285; without the change, the kernel was unloadable ("Can't load kernel") and I didn't even get a loader menu (e.g., to facilitate loading a different kernel).

[delphij]

Referenced wrong review. This was committed as rS337317.