drivers: thermal: cpu_voltage: initialize pointer variables before using it

Initialize cpu freq table pointer to NULL while defining the same.
It avoids a possible use of uninitialized value of this stack pointer
in error path.

Change-Id: If9fb6bfeb836d1f3c81ecd5d9910cf0c76b4a0c5
Signed-off-by: Manaf Meethalavalappu Pallikunhi <manafm@codeaurora.org>