OMAP2+: omap_device/clock: Do not expect an entry in clkdev for opt_clks

The _add_optional_clock_alias function expects an entry
already existing in the clkdev table in the form of
<dev-id=NULL, con-id=role> which might not be the case
always.

Instead, just check if an entry already exists in clkdev
in the <dev-id=dev_name, con-id=role> form, else go ahead
and add one.

Remove any assumption of an entry already existing in clkdev
table in any form.

Since this means, adding a new entry in clkdev if it does
not already exist, and not really adding an 'alias',
also rename the function name
(s/_add_optional_clock_alias/_add_optional_clock_clkdev)
to reflect this.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Reported-by: Sumit Semwal <sumit.semwal@ti.com>
Cc: Sumit Semwal <sumit.semwal@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Partha Basak <p-basak2@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>