Don't use hard-coded 'size' value in snprintf()

This patch changes the passing of "size" to snprintf
from hard-coded (openended) to sizeof(errbuf). This
is bringing to standard with rest of the code where-
ever 'errbuf' is used.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Closes #15003