drivers: mailbox: qti-tcs: Fix incorrect TCS assignment

The TCS configuration is read from the DT, initialize in the same order
in which it is read. The order of the TCS specified in DT matches the
firmware's interpretation of the TCSes.

Change-Id: I8a01f5d8c2db20145ed62329c978b1b02dc49deb
Signed-off-by: Lina Iyer <ilina@codeaurora.org>