dm-pcache: cleanup: fix coding style report by checkpatch.pl

A patch from a few days ago fixed the division issue on 32-bit machines,
but it introduced a coding style problem.

WARNING: Missing a blank line after declarations
+       u32 rem;
+       div_u64_rem(off >> PCACHE_CACHE_SUBTREE_SIZE_SHIFT,
	cache->n_ksets, &rem);

total: 0 errors, 1 warnings, 634 lines checked

Signed-off-by: Dongsheng Yang <dongsheng.yang@linux.dev>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>