[POWERPC] cell/PS3: Always set master run control bit in mfc_sr1_set

At present, running any SPE program on the ps3 will trigger a BUG_ON
when spufs_run_spu tries to clear the master run control bit, as lv1
does not make the master run control available to Linux.

This change makes SPE apps work again by disabling changes to the
master run control on PS3.  Although we don't have the facility to
disable a SPE with supervisor-level privileges, it's better than
hitting the BUG_ON unconditionally.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Acked-by: Masato Noguchi <Masato.Noguchi@jp.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>