EDAC, pnd2: Return proper error value from apl_rd_reg()

Add code comment to make it clear that the fall-through is intentional
and, OR ret with its previous value to avoid overwriting it so that
callers can check the correct return value.
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Cc: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/20170622220535.GA4896@embeddedgus
[ Massage a bit. ]
Signed-off-by: Borislav Petkov <bp@suse.de>

drivers/edac/pnd2_edac.c

@@ -174,8 +174,9 @@ static int apl_rd_reg(int port, int off, int op, void *data, size_t sz, char *na
 	switch (sz) {
 	case 8:
 		ret = sbi_send(port, off + 4, op, (u32 *)(data + 4));
+		/* fall through */
 	case 4:
-		ret = sbi_send(port, off, op, (u32 *)data);
+		ret |= sbi_send(port, off, op, (u32 *)data);
 		pnd2_printk(KERN_DEBUG, "%s=%x%08x ret=%d\n", name,
 					sz == 8 ? *((u32 *)(data + 4)) : 0, *((u32 *)data), ret);
 		break;