staging: ft1000-usb: Remove global flag DSP_loading.

This patch remove global flag DSP_loading which was checked
only on one place. Instead check return value for dsp_reload() function.

Signed-off-by: Marek Belisko <marek.belisko@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>