Fix bug

[mkx171217]

1. using register a0 to pass argument to function puts, not register a1.
2. "jalr ra, puts" would generate a compile error. Shoule be "jal puts" or "jal ra, puts".

[mkx171217]

n/a

[aswaterman]

Thanks - this looks correct to me. I’ll merge now, but would appreciate an ex post facto sanity check from @palmer-dabbelt

[palmer-dabbelt]

Yep, the jalr was nonsense -- sorry that slipped through! This should be jal ra, puts, not jal puts, as jal puts is an alias and we're trying to avoid those in the docs.

Thanks!