Only the following cdevs do not declare an .lseek() operation:

  - Console devices in common/console.c
  - Firmware framework in common/firmware.c
  - JTAG driver in drivers/misc/jtag.c
  - UBI in drivers/mtd/ubi/barebox.c

Of those four, first two are marked DEVFS_IS_CHARACTER_DEV and
implement only .write() operation and the last two don't implement
anything but .ioctl(). While there's probably no meaningful way to use
lseek() against any of those devices, there doesn't seem to be any
harm in allowing it either.

Change devfs_lseek() to ignore absense of .lseek() callback and drop
dev_lseek_default() and all references to it in the codebase.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>