Bluetooth: btmrvl: reset is_suspending flag in failure path

is_suspending flag remains on when host sleep fails to enable. Data
path is unnecessarily blocked after this. This patch ensures to
reset the flag in failure path.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>