Fix C90 declaration order warning in remoteproc

A "declaration-after-statement" warning is generated when building the
remoteproc driver because C90 doesn't allow variables to be declared
after a statement in a scope.

To resolve this, the order of the variables at the start of the
problematic scope have been reordered to comply with C90.

Change-Id: Id7fec564858168fd71cd10af9c99340691484b89
Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>