avoid build warning if CONFIG_IOMMU is not defined

The function vspace_map_io() is only used when CONFIG_IOMMU is defined,
thus the clang build warning "control reaches end of non-void function
[-Wreturn-type]" can be avoided easily when this function only exists
when it is needed.

Signed-off-by: Axel Heider <axelheider@gmx.de>

libsel4vspace/src/arch/arm/mapping.c

diff --git a/libsel4vspace/src/arch/arm/mapping.c b/libsel4vspace/src/arch/arm/mapping.c
index e9d55c2..e3c9003 100644
--- a/libsel4vspace/src/arch/arm/mapping.c
+++ b/libsel4vspace/src/arch/arm/mapping.c
@@ -7,13 +7,13 @@
 #include <autoconf.h>
 #include <vspace/mapping.h>
 
+#ifdef CONFIG_TK1_SMMU
 static seL4_Error vspace_map_io(seL4_CPtr cap, seL4_CPtr iospace_root,
                                 seL4_Word vaddr, UNUSED seL4_Word attr)
 {
-#ifdef CONFIG_TK1_SMMU
     return seL4_ARM_IOPageTable_Map(cap, iospace_root, vaddr);
-#endif
 }
+#endif /* CONFIG_TK1_SMMU */
 
 int vspace_get_iospace_map_obj(UNUSED seL4_Word failed_bits, vspace_map_obj_t *obj)
 {

libsel4vspace/src/arch/x86/mapping.c

diff --git a/libsel4vspace/src/arch/x86/mapping.c b/libsel4vspace/src/arch/x86/mapping.c
index c6f0fc7..436d343 100644
--- a/libsel4vspace/src/arch/x86/mapping.c
+++ b/libsel4vspace/src/arch/x86/mapping.c
@@ -8,13 +8,13 @@
 #include <vspace/mapping.h>
 #include <sel4/arch/mapping.h>
 
+#ifdef CONFIG_IOMMU
 static seL4_Error vspace_map_io(seL4_CPtr cap, seL4_CPtr iospace_root,
                                 seL4_Word vaddr, UNUSED seL4_Word attr)
 {
-#ifdef CONFIG_IOMMU
     return seL4_X86_IOPageTable_Map(cap, iospace_root, vaddr);
-#endif
 }
+#endif /* CONFIG_TK1_SMMU */
 
 int vspace_get_iospace_map_obj(UNUSED seL4_Word failed_bits, vspace_map_obj_t *obj)
 {