clk: msm: clock-a7: Add en_mask entry to a7ssmux struct

Set the en_mask field to 1 for a7ssmux to allow the clock to
be enabled during handoff.

Change-Id: I3669887dd4090c64165348142a1785d3f0c25991
Signed-off-by: Devesh Jhunjhunwala <deveshj@codeaurora.org>