[POWERPC] Trivial ps3 warning fixes

[POWERPC] Trivial ps3 warning fixes

Fixes warnings:

arch/powerpc/platforms/ps3/system-bus.c: In function 'ps3_map_sg':
arch/powerpc/platforms/ps3/system-bus.c:278: warning: unused variable 'i'
arch/powerpc/platforms/ps3/system-bus.c:277: warning: unused variable 'dev'
arch/powerpc/platforms/ps3/setup.c:103: warning: 'prealloc' defined but not used

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>