init/do_mounts.c should #include <linux/initrd.h>

Every file should include the headers containing the externs for its
global code (in this case for rd_doload).

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>