msm: msm_bus: Modify IB aggregation at master

The IB aggregation at master assumed that the sel_clk pointers were set
before trying to access them, but there could be clients that register
but don't do any transaction at all which could lead to data aborts during
the IB aggregation. Change this to directly access the allocated pnode
entry instead of relying on sel_clk pointer.

Change-Id: Iefffdd5ff835496fa54d3de97e416a62735154a2
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>