sf_probe: Merge spi_flash_probe_tail into spi_flash_probe

spi_flash_probe_tail is now only called from spi_flash_probe, hence we
can merge its body into spi_flash_probe.

Reviewed-by: Jagan Teki <jagan@openedev.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Mario Six <mario.six@gdsys.cc>