powerpc/pseries: Advance pfn if section is not present in lmb_is_removable()

In lmb_is_removable(), if a section is not present, it should continue
to test the rest of the sections in the block. But the current code
fails to do so.

Fixes: 51925fb3 ("powerpc/pseries: Implement memory hotplug remove in the kernel")
Cc: stable@vger.kernel.org # v4.1+
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1578632042-12415-1-git-send-email-kernelfans@gmail.com

arch/powerpc/platforms/pseries/hotplug-memory.c

@@ -360,8 +360,10 @@ static bool lmb_is_removable(struct drmem_lmb *lmb)
 
 	for (i = 0; i < scns_per_block; i++) {
 		pfn = PFN_DOWN(phys_addr);
-		if (!pfn_present(pfn))
+		if (!pfn_present(pfn)) {
+			phys_addr += MIN_MEMORY_BLOCK_SIZE;
 			continue;
+		}
 
 		rc = rc && is_mem_section_removable(pfn, PAGES_PER_SECTION);
 		phys_addr += MIN_MEMORY_BLOCK_SIZE;