drivers/net/ns8382x.c: fix GCC 4.6 build warnings

Fix:
ns8382x.c: In function 'ns8382x_check_duplex':
ns8382x.c:704:6: warning: variable 'hun' set but not used
[-Wunused-but-set-variable]

To fix this, we get rid of the NS8382X_DEBUG code and use standard
debug() instead.

This will now trigger a so far undetected warning:
ns8382x.c:780:2: warning: format '%X' expects argument of type
'unsigned int', but argument 2 has type 'long unsigned int' [-Wformat]

Fix that, too.

Signed-off-by: Wolfgang Denk <wd@denx.de>