media: ti-vpe: cal: Fix a NULL pointer dereference in cal_ctx_v4l2_init_formats()

In the Linux kernel, the following vulnerability has been resolved:

media: ti-vpe: cal: Fix a NULL pointer dereference in cal_ctx_v4l2_init_formats()

In cal_ctx_v4l2_init_formats(), devm_kzalloc() is assigned to

ctx->active_fmt and there is a dereference of it after that, which could

lead to NULL pointer dereference on failure of devm_kzalloc().

Fix this bug by adding a NULL check of ctx->active_fmt.

This bug was found by a static analyzer.

Builds with 'make allyesconfig' show no new warnings, and our static

analyzer no longer warns about this code.