efi_loader: add comments on efi_file_from_path() regarding alignment

UEFI specification requires pointers that are passed to protocol member
functions to be aligned.  There's a u16_strdup in that function which
doesn't make sense otherwise  Add a comment so no one removes it
accidentally

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

lib/efi_loader/efi_file.c

@@ -1144,6 +1144,11 @@ struct efi_file_handle *efi_file_from_path(struct efi_device_path *fp)
 			return NULL;
 		}
 
+		/*
+		 * UEFI specification requires pointers that are passed to
+		 * protocol member functions to be aligned.  So memcpy it
+		 * unconditionally
+		 */
 		filename = u16_strdup(fdp->str);
 		if (!filename)
 			return NULL;