[libata] Fix section mismatch: ata_sff_exit

This build error showed up in linux-next tag next-20100820 for ia64:

WARNING: vmlinux.o(.init.text+0x4a952): Section mismatch in reference from the function ata_init() to the function .exit.text:ata_sff_exit()
The function __init ata_init() references
a function __exit ata_sff_exit().
This is often seen when error handling in the init function
uses functionality in the exit path.
The fix is often to remove the __exit annotation of
ata_sff_exit() so it may be used outside an exit section.

Sure enough, dropping the __exit fixes the problem.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>