[MIPS] Fix fallocate on o32 binary compat ABI

MIPS was mistakenly forgetting to use the fallocate compat wrapper, which
I noticed while cleaning up all the duplicate fallocate wrappers.

Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>