power-supply: Don't over-allocate memory for "supplied-from" array

In routine power_supply_check_supplies(), 'cnt' is counting the number of
supplies passed in "power-supplies" field of a node. The value of 'cnt' will
always be one more than the number of supplies after the do-while loop ends. And
so we need to allocate memory for 'cnt - 1' char pointers. But we are allocating
memory for 'cnt' instead.

Fix this by not over-allocating memory.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>