serial: lantiq: Change ltq_w32_mask to asc_update_bits

[ Upstream commit fccf231ae907dc9eb45eb8a9adb961195066b2c6 ]

ltq prefix is platform specific function, asc prefix
is more generic.

Signed-off-by: Songjun Wu <songjun.wu@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 306320034e8f ("serial: lantiq: add missing interrupt ack")
Signed-off-by: Sasha Levin <sashal@kernel.org>