drivers: rpm-smd: move rpm-smd initcall to postcore_initcall_sync

Move the rpm-smd init call from postcore_initcall to
postcore_initcall_sync to sync with the dependent smd driver probe.

Change-Id: I4ea186206516e762d5c0a4796feb7f6579f999d2
Signed-off-by: Raghavendra Kakarla <rkakarla@codeaurora.org>