bus: ti-sysc: Simplify cleanup upon failures in sysc_probe()

The clocks are not yet parsed and prepared until after a successful
sysc_get_clocks(), so there is no need to unprepare the clocks upon
any failure of any of the prior functions in sysc_probe(). The current
code path would have been a no-op because of the clock validity checks
within sysc_unprepare(), but let's just simplify the cleanup path by
returning the error directly.

While at this, also fix the cleanup path for a sysc_init_resets()
failure which is executed after the clocks are prepared.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>