staging: gs_fpgaboot: remove unnecessary return statements

This fixes "void function return statements are not generally useful"
warnings from checkpatch.pl.

Signed-off-by: Michał Bartoszkiewicz <mbartoszkiewicz@gmail.com>
Reviewed-by: Insop Song <insop.song@gainspeed.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>