omap_hdq: fix usecount handling

hdq_usecount was set to zero after a successful read, so
omap_hdq_put could not properly free resources which leads
e.g. to increasing usecounts in lsmod output

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Reviewed-by: Vignesh R <vigneshr@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>