memblock: make virt_to_phys pointer param const

include/mango/memblock.h

@@ -322,7 +322,7 @@ extern int memblock_free_phys(phys_addr_t addr, size_t size);
 
    @param p the pointer to convert.
 */
-extern phys_addr_t memblock_virt_to_phys(void *p);
+extern phys_addr_t memblock_virt_to_phys(const void *p);
 
 /* convert a physical address returned by memblock
    to a virtual pointer.

vm/memblock.c

@@ -488,7 +488,7 @@ void __next_memory_region(
 	it->__idx = ITER_END;
 }
 
-phys_addr_t memblock_virt_to_phys(void *p)
+phys_addr_t memblock_virt_to_phys(const void *p)
 {
 	return (phys_addr_t)p - memblock.m_voffset;
 }