tcm_fc: remove custom hex_to_bin in ft_parse_wwn

This patch converts ft_parse_wwn() to use hex_to_bin() instead of custom
conversion code.

(Andy: Re-add missing strict && isupper(c) check)

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: "Nicholas A. Bellinger" <nab@linux-iscsi.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>