Correct swapped keylocation error messages

This patch corrects a small issue where two error messages
in the code that checks for invalid keylocations were
swapped.

Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #7418