tests/qemu-iotests: Use GNU sed in two more spots where it is necessary

These two spots have been missed in commit 9086c76 ("Rework the
checks and spots using GNU sed") - they need GNU sed, too, since they
are using the "+" address form.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20220309101626.637836-1-thuth@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

tests/qemu-iotests/common.filter

@@ -106,13 +106,13 @@ _filter_hmp()
 # replace block job offset
 _filter_block_job_offset()
 {
-    sed -e 's/, "offset": [0-9]\+,/, "offset": OFFSET,/'
+    gsed -e 's/, "offset": [0-9]\+,/, "offset": OFFSET,/'
 }
 
 # replace block job len
 _filter_block_job_len()
 {
-    sed -e 's/, "len": [0-9]\+,/, "len": LEN,/g'
+    gsed -e 's/, "len": [0-9]\+,/, "len": LEN,/g'
 }
 
 # replace actual image size (depends on the host filesystem)