efi: loader: Make efi_mem static

efi_mem is only referenced in efi_memory.c

Signed-off-by: Bin Meng <bmeng@tinylab.org>
diff --git a/lib/efi_loader/efi_memory.c b/lib/efi_loader/efi_memory.c
index 8f82496..e2ca78d 100644
--- a/lib/efi_loader/efi_memory.c
+++ b/lib/efi_loader/efi_memory.c
@@ -36,7 +36,7 @@
 #define EFI_CARVE_OVERLAPS_NONRAM	-3
 
 /* This list contains all memory map items */
-LIST_HEAD(efi_mem);
+static LIST_HEAD(efi_mem);
 
 #ifdef CONFIG_EFI_LOADER_BOUNCE_BUFFER
 void *efi_bounce_buffer;