aio: remove bare user-triggerable error printk

The user can generate console output if they cause do_mmap() to fail
during sys_io_setup().  This was seen in a regression test that does
exactly that by spinning calling mmap() until it gets -ENOMEM before
calling io_setup().

We don't need this printk at all, just remove it.

Signed-off-by: Zach Brown <zach.brown@oracle.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>