[PATCH] powerpc: Fix call to ibm,client-architecture-support

The code in prom_init.c calling the firmware
ibm,client-architecture-support method on pSeries has a bug where it
fails to properly pass the instance handle of the firmware object when
trying to call a method. Result ranges from the call doing nothing to
the firmware crashing. (Found by Segher, thanks !)

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>