omapfb: fix multiple reference count leaks due to pm_runtime_get_sync

On calling pm_runtime_get_sync() the reference count of the device
is incremented. In case of failure, decrement the
reference count before returning the error.

Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Cc: kjlu@umn.edu
Cc: wu000273@umn.edu
Cc: Allison Randal <allison@lohutok.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Enrico Weigelt <info@metux.net>
cc: "Andrew F. Davis" <afd@ti.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Alexios Zavras <alexios.zavras@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200614030528.128064-1-pakki001@umn.edu