GCC4.6: Squash warnings in fec_mxc.c

fec_mxc.c: In function 'fec_mii_setspeed':
fec_mxc.c:112:2: warning: format '%#lx' expects type 'long unsigned int', but
argument 2 has type 'u32'
fec_mxc.c: In function 'fec_recv':
fec_mxc.c:632:2: warning: format '%x' expects type 'unsigned int', but argument
2 has type 'long unsigned int'

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Mike Frysinger <vapier@gentoo.org>