clk: ti: Use int to check return value from of_property_count_elems_of_size()

This function can return a negative number when it fails, but res->sets
is at most a u16 which can't hold that negative number. Let's store the
result into an int, ret, and then assign that to res->sets when it works
to avoid this logical impossibility.

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