usb: gadget: f_hid: wake up readers on disable/unbind

Similar to how it is done in the write path.

Add a disabled flag to track the function state and use it to exit the read
loops to ensure no readers get stuck when the function is disabled/unbound,
protecting against corruption when the waitq and spinlocks are reinitialized
in hidg_bind().

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Link: https://lore.kernel.org/r/20250318152207.330997-1-peter@korsgaard.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>