sh: remove spurious circular inclusion from asm/smp.h

Commit 0cd39f46 added inclusion of smp.h to lockdep.h,
creating a circular include dependency where arch/sh's asm/smp.h in
turn includes spinlock.h which depends on lockdep.h. Since our
asm/smp.h does not actually need spinlock.h, just remove it.

Fixes: 0cd39f46 ("locking/seqlock, headers: Untangle the spaghetti monster")
Tested-by: Rob Landley <rob@landley.net>
Signed-off-by: Rich Felker <dalias@libc.org>