MAINTAINERS: Remove phy-stih41x-usb.c entry from STi arch

Remove this driver as the IP is only found on STiH415/6
silicon, and support for these SoC's is being removed
from the kernel.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Cc: <kishon@ti.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>