sandbox: Make map_to_sysmem() use a constant pointer

Very often a constant pointer is passed to this function, so we should
declare this, since map_to_sysmem() does not change the pointer.
Signed-off-by: NSimon Glass <sjg@chromium.org>

arch/sandbox/include/asm/io.h

@@ -38,6 +38,6 @@ static inline void unmap_sysmem(const void *vaddr)
 }
 
 /* Map from a pointer to our RAM buffer */
-phys_addr_t map_to_sysmem(void *ptr);
+phys_addr_t map_to_sysmem(const void *ptr);
 
 #endif

include/common.h

@@ -923,7 +923,7 @@ static inline void unmap_sysmem(const void *vaddr)
 {
 }
 
-static inline phys_addr_t map_to_sysmem(void *ptr)
+static inline phys_addr_t map_to_sysmem(const void *ptr)
 {
 	return (phys_addr_t)(uintptr_t)ptr;
 }