depmod: add missing "else" clause

It occurred to an openSUSE user that our mkinitrd would throw a
warning when used with kmod:

libkmod: conf_files_list: unsupported file mode /dev/null: 0x21b6

Grepping for the error message revealed that there might be a missing
"else" keyword here, since it is unusual to put an "if" directly after
closing brace.