Fix ioctl numbers on BSDs

`<sys/ioccom.h>` defines `IOC_OUT` as `0x40000000UL`. But this is "out"
from the perspective of the kernel, not the application. So this
corresponds to `READ` rather than `WRITE`.

Tested with Smithay/drm-rs#180. This also seems
to be correct for NetBSD and OpenBSD.

src/ioctl/bsd.rs

@@ -19,6 +19,6 @@ pub(super) const fn compose_opcode(
 }
 
 pub const NONE: RawOpcode = 0x2000_0000;
-pub const WRITE: RawOpcode = 0x4000_0000;
-pub const READ: RawOpcode = 0x8000_0000;
+pub const READ: RawOpcode = 0x4000_0000;
+pub const WRITE: RawOpcode = 0x8000_0000;
 pub const IOCPARAM_MASK: RawOpcode = 0x1FFF;