msm: dsps: Return 0 on success in dsps_probe()

A recent patch to this file accidentally removed the return 0 at
the bottom of this function causing the probe to unconditionally
fail. Add it back so that probe works correctly.

Change-Id: I8743eeec9899168b27338a22475c93b6b6b5be3a
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>