media: qcom: camss: Functionally decompose CSIPHY clock lookups

The csiphyX_timer and csiX_phy values need not be hard-coded. We can
functionally decompose the string matching inside of a loop.

Static string values are brittle, difficult to extend and not required
anyway since the camss->res->csiphy_num value informs us of the number
of CSIPHYs and hence the set of potential clocks for a given CSIPHY.

In simple terms if we have five CSIPHYs we can have no more and no less
than five csiphy_timer clocks. Similarly csi_phy core clocks have a 1:1
relationship with the PHY they clock.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>