clk: shmobile: Fix MSTP clock array initialization

The clks member of the clk_onecell_data structure should
point to a valid clk array (no NULL entries allowed),
and the clk_num should be equal to the number
of elements in the clks array.

The MSTP driver fails to satisfy the above conditions.
The clks array may contain NULL entries if not all
clock-indices are initialized in the device tree.
Thus, if the clock indices are interleaved we end up
with NULL pointers in-between.

The other problem is the driver uses maximum clock index
as the number of clocks, which is incorrect (less than
the actual number of clocks by 1).

Fix the first issue by pre-setting the whole clks array
with ERR_PTR(-ENOENT) pointers instead of zeros; and
use maximum clkidx + 1 as the number of clocks to fix
the other one.

This should make of_clk_src_onecell_get() return the following:
* valid clk pointers for all clocks registered;
* ERR_PTR(-EINVAL) if (idx >= clk_data->clk_num);
* ERR_PTR(-ENOENT) if the clock at the selected index was not
  initialized in the device tree (and was not registered).

Changes in V2:
* removed brackets from the one-line for loop

Signed-off-by: Valentine Barshak <valentine.barshak@cogentembedded.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Mike Turquette <mturquette@linaro.org>