UBIFS: increase dumps loglevel

Most of the time we use the dumping function to dump something in case
of error. We use 'KERN_DEBUG' printk level, and the drawback is that users
do not see them in the console, while they see the other error messages
in the console. The result is that they send bug reports which does not
contain a lot of useful information. This patch changes the printk level
of the dump functions to 'KERN_ERR' to correct the situation.

I documented it in the MTD web site that people have to send the 'dmesg' output
when submitting bug reposts - it did not help.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>