drivers/net/uli526x.c: fix syntax error

Fix error detected by cppcheck:

[drivers/net/uli526x.c:551]: (error) printf format string requires 3
parameters but only 2 are given.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Roy Zang <tie-fei.zang@freescale.com>