Fix hd command so it doesn't error out on EOF

hd would error out on files that were not a multiple of its read
buffer size (4096).  For example:
Read error on init.rc, offset 17040 len 4096, No such file or directory

The fix is to stop reading on EOF instead of treating it as an
error.

Change-Id: Ie7f4216e08835150f2f5784e77bb9e2190b0def4
Signed-off-by: Scott Anderson <saa@google.com>