bfd: cast BFD_ALIGN to fix clang error on mips

error: implicit conversion from 'bfd_vma' (aka 'unsigned long long')
to 'int' changes value from 18446744073709551615 to -1

return BFD_ALIGN (ret, 16);
~~~~~~ ^~~~~~~~~~~~~~~~~~~

note: expanded from macro 'BFD_ALIGN'

: ~ (bfd_vma) 0)
  ^~~~~~~~~~~~~

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