msm_serial_hs: Fix register access issue

Crash is seen in the dump_uart_hs_registers()
function due to improper array offset passed to
access the registers. This patch corrects the
array index during the register access.

CRs-Fixed: 576874
Change-Id: Iba54b72cefa01ff855b17e981aa4dd2886126003
Signed-off-by: Dilip Kota <c_dkota@codeaurora.org>