EDAC, sb_edac: Fix signedness bugs in *_get_ha() functions

A static checker gave the following warnings:

  drivers/edac/sb_edac.c:1030 ibridge_get_ha() warn: signedness bug returning '(-22)'
  drivers/edac/sb_edac.c:1037 knl_get_ha() warn: signedness bug returning '(-22)'

Both because the functions are declared to return a "u8", but try to
return -EINVAL for the error case.

Fix by returning 0xff (since the caller doesn't look at, or pass on, the
return value).
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Cc: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/20180914201905.GA30946@agluck-deskSigned-off-by: Borislav Petkov <bp@suse.de>

drivers/edac/sb_edac.c

@@ -1027,14 +1027,14 @@ static u8 ibridge_get_ha(u8 bank)
 	case 9 ... 16:
 		return (bank - 9) / 4;
 	default:
-		return -EINVAL;
+		return 0xff;
 	}
 }
 
 /* Not used, but included for safety/symmetry */
 static u8 knl_get_ha(u8 bank)
 {
-	return -EINVAL;
+	return 0xff;
 }
 
 static u64 haswell_get_tolm(struct sbridge_pvt *pvt)