efi_loader: missing include in efi_string.c

To avoid diverging function definitions we need to include efi_loader.h.

Fixes: fe179d7fb5 ("efi_loader: Add size checks to efi_create_indexed_name()")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

lib/efi_loader/efi_string.c

@@ -7,6 +7,7 @@
 
 #include <common.h>
 #include <charset.h>
+#include <efi_loader.h>
 
 /**
  * efi_create_indexed_name - create a string name with an index