Slimbus: Correct the conditional check during channel removal

Use actual channel number to check if the channel to be
removed is present in the define_chan list before removing
it, instead of using the internal channel number used by
the frame work.

Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>