clk: ti: dra7xx: mark MCAN clock as DRA76x only

This clock entry does not exist on any other devices except DRA76,
so mark it as specific to that SoC only.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Link: https://lkml.kernel.org/r/20200430083640.8621-3-t-kristo@ti.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>