USB: Fix s3c-hsotg build following Samsung platform header moves

Fix a reference to regs-sys.h got missed in the reorganisation of
the Samsung platform headers targetted for 2.6.34.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>