[SPARC64]: Solidify check in cheetah_check_main_memory().

Need to make sure the address is below high_memory before
passing it to kern_addr_valid().
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc64/kernel/traps.c

@@ -1333,6 +1333,9 @@ static int cheetah_check_main_memory(unsigned long paddr)
 {
 	unsigned long vaddr = PAGE_OFFSET + paddr;
 
+	if (vaddr > high_memory)
+		return 0;
+
 	return kern_addr_valid(vaddr);
 }