[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: David S. Miller <[e-mail]>

arch/sparc64/kernel/traps.c

···
 {
 	unsigned long vaddr = PAGE_OFFSET + paddr;
 
+	if (vaddr > high_memory)
+		return 0;
+
 	return kern_addr_valid(vaddr);
 }