msm_serial_hs: Disable RFR line and auto RFR in set_termios

This change disables the RFR line during set_termios call so that
the remote side does not send data during this call and thus prevents
data omission and corruption.

CRs-Fixed: 557659
Change-Id: I0708168b858a42d102ad3e5ebcbd6ca33943c8b1
Signed-off-by: Naveen Kaje <nkaje@codeaurora.org>