x86/boot: Use current_stack_pointer to avoid asm() in init_heap()

Use current_stack_pointer to avoid asm() in the calculation of
stack_end in init_heap(). The new code is more readable and
results in exactly the same object file.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240520083011.135342-1-ubizjak@gmail.com

arch/x86/boot/main.c

@@ -119,9 +119,8 @@ static void init_heap(void)
 	char *stack_end;
 
 	if (boot_params.hdr.loadflags & CAN_USE_HEAP) {
-		asm("leal %n1(%%esp),%0"
-		    : "=r" (stack_end) : "i" (STACK_SIZE));
-
+		stack_end = (char *)
+			(current_stack_pointer - STACK_SIZE);
 		heap_end = (char *)
 			((size_t)boot_params.hdr.heap_end_ptr + 0x200);
 		if (heap_end > stack_end)