Input: edt-ft5x06 - fix use-after-free in debugfs teardown

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

Input: edt-ft5x06 - fix use-after-free in debugfs teardown

The commit 68743c500c6e ("Input: edt-ft5x06 - use per-client debugfs

directory") removed the manual debugfs teardown, relying on the I2C core

to handle it. However, this creates a window where debugfs files are

still accessible after edt_ft5x06_ts_teardown_debugfs() frees

tsdata->raw_buffer.

To prevent a use-after-free, protect the freeing of raw_buffer with the

device mutex and set raw_buffer to NULL. The debugfs read function

already checks if raw_buffer is NULL under the same mutex, so this

safely avoids the use-after-free.