Check for valid parameters in check rate. Else, we end up getting
errors.

This occurs as part of the inital clock tree update of child clock
nodes where new_rate could be 0 for non functional clocks.

Fixes: 9ac33b0c (" CLK: TI: Driver for DRA7 ATL (Audio Tracking Logic)")
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>