msm_serial_hs: Enable clocks for register writes in probe

The msm_serial_hs driver performs register writes without enabling
either the core or iface clocks. As a result, these writes do not
go through. Fix this.

Change-Id: Ia1a215818fa09802d0ea6e4d06db0b4842dabd27
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>