[NFC] Adjust "invalid.ll.bc" tests to check for AttrKind #255 not #63

We are about to add enum attributes with AttrKind numbers >= 63. This
means we cannot use AttrKind #63 to test for an invalid attribute number
in the RAW format anymore. This patch changes the number of an invalid
attribute to #255. There is no change to the character of the tests.

Differential Revision: https://reviews.llvm.org/D64531

llvm-svn: 365722