Fix the following coccicheck warning:

./arch/arm/mach-omap2/pm-debug.c:171:0-23: WARNING: pwrdm_suspend_fops
should be defined with DEFINE_DEBUGFS_ATTRIBUTE.
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>