qemu-iotests: fix pattern for write test

The write pattern value 0axb is invalid and evaluates to 0,
so the read check (which uses a correct value of 0xab) will fail.

This failure will only be detected with a separate patch for
qemu-io. Without it, qemu-io cannot interpret hex values
and always uses a pattern value of 0.
Signed-off-by: NStefan Weil <weil@mail.berlios.de>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

tests/qemu-iotests/002

@@ -61,7 +61,7 @@ $QEMU_IO -c "read -pP 0xa 0 $size" $TEST_IMG | _filter_qemu_io
 
 echo
 echo "unaligned pwrite"
-$QEMU_IO -c 'write -pP 0axb 66 42' $TEST_IMG | _filter_qemu_io
+$QEMU_IO -c 'write -pP 0xab 66 42' $TEST_IMG | _filter_qemu_io
 
 echo
 echo "verify pattern"