optee: Fix memory leak when failing to register shm pages

Free the previously allocated pages when we encounter an error condition
while attempting to register the pages with the secure world.

Fixes: a249dd20 ("tee: optee: Fix dynamic shm pool allocations")
Fixes: 5a769f6f ("optee: Fix multi page dynamic shm pool alloc")
Cc: stable@vger.kernel.org
Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>