clk: msm: clock-local2: Fix get_rate ops for branch clock

For branch clocks having aggr_sibling_rates flag as set, get_rate()
always returns the parents rate despite the branch clocks prepare
status. Fix the same by adding a check for branch prepare status
and aggr_sibling_rates flag value.

Change-Id: If0ba62e178f14bc5fd8ec6007a67538a9b97285b
Signed-off-by: Amit Nischal <anischal@codeaurora.org>