boot: fdt: Change type of env_get_bootm_low() to phys_addr_t

Change type of ulong env_get_bootm_low() to phys_addr_t env_get_bootm_low().
The PPC/LS systems already treat env_get_bootm_low() result as phys_addr_t,
while the function itself still returns ulong. This is potentially dangerous
on 64bit systems, where ulong might not be large enough to hold the content
of "bootm_low" environment variable. Fix it by using phys_addr_t, similar to
what env_get_bootm_size() does, which returns phys_size_t .

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reported-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
diff --git a/boot/bootm.c b/boot/bootm.c
index d071537..032f5a4 100644
--- a/boot/bootm.c
+++ b/boot/bootm.c
@@ -242,13 +242,13 @@
 #ifdef CONFIG_LMB
 static void boot_start_lmb(struct bootm_headers *images)
 {
-	ulong		mem_start;
+	phys_addr_t	mem_start;
 	phys_size_t	mem_size;
 
 	mem_start = env_get_bootm_low();
 	mem_size = env_get_bootm_size();
 
-	lmb_init_and_reserve_range(&images->lmb, (phys_addr_t)mem_start,
+	lmb_init_and_reserve_range(&images->lmb, mem_start,
 				   mem_size, NULL);
 }
 #else