Fix zpl_mknod() return values

The zpl_mknod() function was incorrectly negating its return value.
This doesn't cause any problems in the success case, but it does
prevent us from returning the correct error code for a failure.
The implementation of this function is now consistent with all
the other zpl_* functions.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1717

module/zfs/zpl_inode.c

@@ -143,7 +143,7 @@ zpl_mknod(struct inode *dir, struct dentry *dentry, zpl_umode_t mode,
 	crfree(cr);
 	ASSERT3S(error, <=, 0);
 
-	return (-error);
+	return (error);
 }
 
 static int