HID: change return type of report_fixup() to const

HID: change return type of report_fixup() to const

By allowing the drivers to return a "const *" they can constify their
static report arrays.
This makes it clear to driver authors that the HID core will not modify
those reports and they can be reused for multiple devices.
Furthermore security is slightly improved as those reports are protected
against accidental or malicious modifications.

[bentiss: fixup hid-cougar.c and hid-multitouch.c for latest version of
the master branch]

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://patch.msgid.link/20240803-hid-const-fixup-v2-6-f53d7a7b29d8@weissschuh.net
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>