libaio: Fix MIPS system call interface

libaio: Fix MIPS system call interface

The io_syscallX wrappers in syscall-mips.h discard error return status
by overwriting the value returned in v0 from the system call with -1.

Modify this behavior by returning the negative of the return value on
error (as identified by a3 != 0). This convention is consistent with
the behavior observed in syscall-ppc.h.

For a description of the MIPS system call interface, see:

http://www.linux-mips.org/wiki/Syscall

(From OE-Core rev: 0d8f50c33e5ff71dc17121b5c293718a8ad602bd)

Signed-off-by: Phil Staub <Phil.Staub@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>