POWERPC: fix typo in pseries/power.c

Introduced by commit 79393fc4

 ("kobject:
convert pseries/power.c to kobj_attr interface").

sys_create_file takes a "struct attrbute *" not a "struct kobj_addribute *".

arch/powerpc/platforms/pseries/power.c: In function 'apo_pm_init':
arch/powerpc/platforms/pseries/power.c:78: warning: passing argument 2 of 'sysfs_create_file' from incompatible pointer type

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Paul Mackerras <paulus@au.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>