PM / clk: signedness bug in of_pm_clk_add_clks()

"count" needs to be signed for the error handling to work.  I made "i"
signed as well so they match.

Fixes: 02113ba9

 (PM / clk: Add support for obtaining clocks from device-tree)
Cc: 4.6+ <stable@vger.kernel.org> # 4.6+
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>