cmd_mem.c: Fix warning when CONFIG_CMD_MEMTEST is not set

mem_test_quick and mem_test_alt functions are only called by
do_mem_mtest, so move them under the #ifdef

Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/common/cmd_mem.c b/common/cmd_mem.c
index 53572f7..64dd76a 100644
--- a/common/cmd_mem.c
+++ b/common/cmd_mem.c
@@ -631,6 +631,7 @@
 }
 #endif /* CONFIG_LOOPW */
 
+#ifdef CONFIG_CMD_MEMTEST
 static ulong mem_test_alt(vu_long *buf, ulong start_addr, ulong end_addr,
 			  vu_long *dummy)
 {
@@ -910,7 +911,6 @@
 	return 0;
 }
 
-#ifdef CONFIG_CMD_MEMTEST
 /*
  * Perform a memory test. A more complete alternative test can be
  * configured using CONFIG_SYS_ALT_MEMTEST. The complete test loops until