misc: fastrpc: fix double refcounting on dmabuf

misc: fastrpc: fix double refcounting on dmabuf

dma buf refcount has to be done by the driver which is going to use the fd.
This driver already does refcount on the dmabuf fd if its actively using it
but also does an additional refcounting via extra ioctl.
This additional refcount can lead to memory leak in cases where the
applications fail to call the ioctl to decrement the refcount.

So remove this extra refcount in the ioctl

More info of dma buf usage at drivers/dma-buf/dma-buf.c

Reported-by: Mayank Chopra <mak.chopra@codeaurora.org>
Reported-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Tested-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20190829092926.12037-5-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>