msm_serial_hs_lite: Use aliases for setting line number

Using device tree aliases rather than the cell-index
property is the more commonly-used method of setting the
line number of a serial device.

Change-Id: I58a70fa971848cd3e0530fb5786a0aa2243188eb
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>