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.

CRs-Fixed: 555260
Change-Id: I4c9521f7d228ca43c155fedf2c9ba5b8f86e2d3a
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>