driver/net/rtl8139: remove debug print

debug print delays reset of the driver. Finally I see
bunch of "rx error FFFF" errors in the screen. CI can
not handle many prints. While network works fine there

Reproduced with:
make CROSS_COMPILE=sh2-linux- r2dplus_defconfig all
qemu-system-sh4 -M r2d -nographic -serial null \
-serial mon:stdio -net user,tftp=`pwd` \
-net nic,model=rtl8139 -kernel ./u-boot.bin

Signed-off-by: Maxim Uvarov <maxim.uvarov@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>