mtd: spi-nor-core: Call mtd_erase_callback() from spi_nor_erase()

mtd: spi-nor-core: Call mtd_erase_callback() from spi_nor_erase()

The spi_nor_erase() function does not call mtd_erase_callback() as it
should.

The mtdpart code currently implements the subtraction of partition
offset in mtd_erase_callback().

This results in partition offset being added prior calling
spi_nor_erase(), but not subtracted back on return. The result is that
the `mtd erase` command does not erase the whole partition, only some of
it's blocks:

  => mtd erase "Rescue system"
  Erasing 0x00000000 ... 0x006fffff (1792 eraseblock(s))
  jedec_spi_nor spi-nor@0: at 0x100000, len 4096
  jedec_spi_nor spi-nor@0: at 0x201000, len 4096
  jedec_spi_nor spi-nor@0: at 0x302000, len 4096
  jedec_spi_nor spi-nor@0: at 0x403000, len 4096
  jedec_spi_nor spi-nor@0: at 0x504000, len 4096
  jedec_spi_nor spi-nor@0: at 0x605000, len 4096
  jedec_spi_nor spi-nor@0: at 0x706000, len 4096

This is obviously wrong.

Add proper calling of mtd_erase_callback() into the spi_nor_erase()
function.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reported-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
Tested-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>