rpmsg: resmgr: disable aux_clk_src in case of error

rpmsg: resmgr: disable aux_clk_src in case of error

If set_rate of aux_clk failed aux_clk_src was being left
enabled affecting the core OFF, fix the same.

Also avoid changing the return value of clk_set_rate.

Change-Id: I897d0669b43bf75ae49e9119ebfadf531bd585d5
Reported-by: Huzefa Kankroliwala <huzefank@ti.com>
Reported-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Miguel Vadillo <vadillo@ti.com>