misc: fastrpc: increase maximum session count

The SC8280XP platform uses 14 sessions for the compute DSP so increment
the maximum session count.

Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20220829080531.29681-4-johan+linaro@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>