Fix calloc(3) arguments order

calloc(3) takes `nelem` (or `nmemb` in glibc) first, and then size of
elements.  No difference expected for having these in reverse order,
however should follow the standard.

http://pubs.opengroup.org/onlinepubs/009695399/functions/calloc.html

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@osnexus.com>
Closes #7405

tests/zfs-tests/cmd/mkfile/mkfile.c

@@ -194,7 +194,7 @@ main(int argc, char **argv)
 				if (buf)
 					free(buf);
 				bufsz = (size_t)st.st_blksize;
-				buf = calloc(bufsz, 1);
+				buf = calloc(1, bufsz);
 				if (buf == NULL) {
 					(void) fprintf(stderr, gettext(
 					    "Could not allocate buffer of"