diag: Ignore connecting to invalid hsic channel

Diag currently has support for 4 hsic channels. Added checks to
discard connections to invalid hsic channel in diag driver.

Change-Id: I3536cc94839bcaa97ccd21d4a0423b98634fd660
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>