drm/i915/bios: fix a memory leak in generate_lfp_data_ptrs

When (size != 0 || ptrs->lvds_ entries != 3), the program tries to
free() the ptrs. However, the ptrs is not created by calling kzmalloc(),
but is obtained by pointer offset operation.
This may lead to memory leaks or undefined behavior.

Fix this by replacing the arguments of kfree() with ptrs_block.

Fixes: a87d0a84 ("drm/i915/bios: Generate LFP data table pointers if the VBT lacks them")
Signed-off-by: Xia Fukun <xiafukun@huawei.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221125063428.69486-1-xiafukun@huawei.com