HiSax: fix error checking for hisax_register()]

This patch (as875) adds error-checking to the callers of hisax_register().
It also changes an error pathway in that routine, making it return an error
code rather than 0.

This fixes Bugzilla #7960.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Karsten Keil <kkeil@suse.de>
Cc: Martin Bachem <info@colognechip.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>