hid_bpf_input_report() is already marked to be used in sleepable context
only. So instead of hammering with timers the device to hopefully get
an available slot where the device is not sending events, we can make
that kfunc wait for the current event to be terminated before it goes in.

This allows to work with the following pseudo code:

in struct_ops/hid_device_event:
  - schedule a bpf_wq, which calls hid_bpf_input_report()
  - once this struct_ops function terminates, hid_bpf_input_report()
    immediately starts before the next event

Link: https://patch.msgid.link/20240626-hid_hw_req_bpf-v2-9-cfd60fb6c79f@kernel.orgAcked-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>