ubi: block: Reduce warning print to info for static volumes

If volume size is not multiple of the sector size 512 a warning is
printed saying that the last non-sector aligned bytes will be ignored.

This should be valid for resizable volumes, but when creating static
volumes which are read only this will always be printed even if the
unaligned data is deliberate.

The message is still valid but the severity should be lowered for static
volumes.

Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
Signed-off-by: Richard Weinberger <richard@nod.at>