riscv locore.S: load constant prior to loop

[freebsdphab-AX9_cmx.ietfng.org]

Summary

A very minor micro-optimization; t0 is not clobbered between the loop top and bottom and there appear to be no other branches to this label.

[mhorne]

Hi, thank you for the patch. It looks good.

In the future, please upload diffs with full context. It makes them easier to review. To do so, run git show -U99999, or use the arcanist tool.

Could you confirm your name and email address for the "Submitted by:" tag in the commit?

Submitted by: Nathaniel Filardo <[e-mail]>

[freebsdphab-AX9_cmx.ietfng.org]

Yes, that's a fine "Submitted by".

Thanks for the tip about full context.