Linux 6.6 compat: fix implicit conversion error with debug build

With Linux v6.6.0 and GCC 12, when debug build is configured,
implicit conversion error is raised while converting
'enum <anonymous>' to 'boolean_t'. Use 'B_TRUE' instead of
'true' to fix the issue.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Pavel Snajdr <[email protected]>
Reviewed-by: Brian Atkinson <[email protected]>
Signed-off-by: Umer Saleem <[email protected]>
Closes openzfs#15489

Author: Umer Saleem

module/os/linux/zfs/zfs_vfsops.c

@@ -1488,7 +1488,7 @@ zfs_domount(struct super_block *sb, zfs_mnt_t *zm, int silent)
 	 * read-only flag, pretend it was set, as done for snapshots.
 	 */
 	if (!canwrite)
-		vfs->vfs_readonly = true;
+		vfs->vfs_readonly = B_TRUE;
 
 	error = zfsvfs_create(osname, vfs->vfs_readonly, &zfsvfs);
 	if (error) {