cfi_flash: Simplify flash_get_info()

This patch removes an unecessary check in the return statement. This is
not needed, since "info" is initializes to NULL. And "info" will not be
written to again, if the flash address is not found.

Additionally "info" is not initialized to "0" but to "NULL".

Signed-off-by: Stefan Roese <sr@denx.de>