Make check_signature depend on CONFIG_HAS_IOMEM

This should avoid build problems on architectures without a "readb()",
that got bitten by check_signature() being uninlined.

Noted by Heiko Carstens.

Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Makefile

@@ -13,15 +13,15 @@ lib-$(CONFIG_SMP) += cpumask.o
 lib-y	+= kobject.o kref.o kobject_uevent.o klist.o
 
 obj-y += div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
-	 bust_spinlocks.o hexdump.o check_signature.o
+	 bust_spinlocks.o hexdump.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG
 CFLAGS_kobject_uevent.o += -DDEBUG
 endif
 
 obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
-obj-$(CONFIG_HAS_IOMEM) += iomap_copy.o devres.o
+obj-$(CONFIG_HAS_IOMEM) += iomap_copy.o devres.o check_signature.o
 obj-$(CONFIG_DEBUG_LOCKING_API_SELFTESTS) += locking-selftest.o
 obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock_debug.o
 lib-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o