Revert "io_uring: don't use int for ABI"

This reverts commit b0878a23 which is
commit cf73d997 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I2e4843aaac11c3013173035d5c619e4123e87b43
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>