Consistently use MAX_ERRNO when checking for errors in __syscall_return().

[ralf@linux-mips.org: build fix]
Signed-off-by: NRandy Dunlap <rdunlap@xenotime.net>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>