[POWERPC] celleb: Fix parsing of machine type hack command line option

This is a bugfix to install Fedora Core 6 by using kernel
command line 'celleb_machine_type_hack=CHRP'.

Yes, this is a one-character fix to add forgotten '='.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Signed-off-by: Paul Mackerras <paulus@samba.org>