[ARM] Osiris: Fix double initialisation in machine block

The .init_machine entry in mach-osiris.c had the same entry
twice, so remove one definition to fix the following warning
from sparse:

mach-osiris.c:416:3: warning: Initializer entry defined twice
mach-osiris.c:418:3:   also defined here

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>