msm: scm: Fix improper register assignment

Assign the registers used in the inline assembly immediately
before the inline assembly block. This ensures the compiler
doesn't optimize away dead register assignments when it
shouldn't.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: David Brown <davidb@codeaurora.org>