usb: gadget: diag: Add kref_put_spinlock_irqsave API

f_diag driver uses kref_put_spinlock_irqsave() API which is
not available now. This change adds this API to allow existing
functionality until other mechnism is found to replace usage
of this API.

Change-Id: I2889936f4293d6eb1286807af5cfc089e4aec150
Signed-off-by: Mayank Rana <mrana@codeaurora.org>