MFC r289055 (by mjg@):

linux: fix handling of out-of-bounds syscall attempts

Due to an off by one the code would read an entry past the table, as
opposed to the last entry which contains the nosys handler.

This fixes my fault.

MFC r289058 (by cem@):

Fix missing semi-colon from r289055.

MFC r289768 (by jhb@):

Merge r289055 to amd64/linux32:

linux: fix handling of out-of-bounds syscall attempts

Due to an off by one the code would read an entry past the table, as
opposed to the last entry which contains the nosys handler.