correct arguments for hexdump

OBS-URL: https://build.opensuse.org/package/show/openSUSE:Tools/build-compare?expand=0&rev=249

build-compare.spec

@@ -21,7 +21,7 @@ Summary:        Build Result Compare Script
 License:        GPL-2.0+
 Group:          Development/Tools/Building
 Url:            https://github.com/openSUSE/build-compare
-Version:        20180528T152809.3cec12e
+Version:        20180529T215607.c58679f
 Release:        0
 Source1:        COPYING
 Source2:        same-build-result.sh

pkg-diff.sh

@@ -307,8 +307,8 @@ diff_two_files()
   mkfifo -m 0600 $pn
   offset=$(( ($offset >> 6) << 6 ))
   length=512
-  hexdump -C -s $offset -l $length old/$file > $po &
-  hexdump -C -s $offset -l $length new/$file > $pn &
+  hexdump -C -s $offset -n $length old/$file > $po &
+  hexdump -C -s $offset -n $length new/$file > $pn &
   diff -u $po $pn | $buildcompare_head
   rm -f $po $pn
   return 1