Blackfin: drop dead flash_probe call

There are no CONFIG_{BLK,CHR}_DEV_FLASH Kconfig options, and there is no
flash_probe() function, so not really sure what this code is all about.
Seems to be dead code that stretches way back to the start of the Blackfin
port.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>