clk: bcm: Allow rate change propagation to PLLH_AUX on VEC clock

The VEC clock requires needs to be set at exactly 108MHz. Allow rate
change propagation on PLLH_AUX to match this requirement wihtout
impacting other IPs (PLLH is currently only used by the HDMI encoder,
which cannot be enabled when the VEC encoder is enabled).

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>