Include sys/types.h in devid.h

This is needed for musl libc

Signed-off-by: Carlo Landmeter <clandmeter@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4454

lib/libspl/include/devid.h

@@ -27,6 +27,7 @@
 #ifndef _LIBSPL_DEVID_H
 #define	_LIBSPL_DEVID_H
 
+#include <sys/types.h>
 #include <stdlib.h>
 
 typedef int ddi_devid_t;