serial: xilinx_uartps: Use helper function hrtimer_update_function()

serial: xilinx_uartps: Use helper function hrtimer_update_function()

[ Upstream commit eee00df8e1f1f5648ed8f9e40e2bb54c2877344a ]

The field 'function' of struct hrtimer should not be changed directly, as
the write is lockless and a concurrent timer expiry might end up using the
wrong function pointer.

Switch to use hrtimer_update_function() which also performs runtime checks
that it is safe to modify the callback.

Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/af7823518fb060c6c97105a2513cfc61adbdf38f.1738746927.git.namcao@linutronix.de
Stable-dep-of: 267ee93c417e ("serial: xilinx_uartps: fix rs485 delay_rts_after_send")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>