md: raid1: kill warning on powerpc_pseries

This patch kills the warning reported on powerpc_pseries,
and actually we don't need the initialization.

	After merging the md tree, today's linux-next build (powerpc
	pseries_le_defconfig) produced this warning:

	drivers/md/raid1.c: In function 'raid1d':
	drivers/md/raid1.c:2172:9: warning: 'page_len$' may be used uninitialized in this function [-Wmaybe-uninitialized]
	     if (memcmp(page_address(ppages[j]),
	         ^
	drivers/md/raid1.c:2160:7: note: 'page_len$' was declared here
	   int page_len[RESYNC_PAGES];
       ^

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Shaohua Li <shli@fb.com>