msm: rpm-smd: return probe success when standalone flag is defined

rpm-smd driver returning -EPROBE_DEFER when "standalone" flag is
defined in DT. Due to this rpm-smd driver keeps probe defer and
will never succeed. It makes clients of rpm-smd drivers to defer
their probe when clients call the rpm-smd exported APIs. To avoid
this return success when "standalone" flag is defined.

Change-Id: I9aefb33902bfff36c038a3d7a35d7fe6bf64799a
Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>