phram: cleanup error handling and associated messages

The error handling in the phram driver is pretty bad -- in many places,
errors are silently ignored or logged, but then still ignored in the
return value.  So convert all of the code to pass back the correct return
value and log error messages properly (and using the new pr_fmt() helper).

If everything does go smoothly, rather than exit silently, dump a helpful
info message like pretty much every other MTD driver does.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Joern Engel <joern@logfs.org>

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>