futex: Fix additional regressions

Naresh reported another architecture that was broken by the same typo that
was already fixed for three architectures: mips also refers to the
futex_atomic_op_inuser_local() function by the wrong name and runs into a
missing closing '}' as well.

Going through the source tree the same typo was found in the documentation
as well as in the xtensa code, both of which ended up escaping the
regression testing so far. In the case of xtensa, it appears that the
broken code path is only used when building for platforms that are not
supported by the default gcc configuration, so they are impossible to test
for with default setups.

After going through these more carefully and fixing up the typos, all
architectures have been build-tested again to ensure that this is now
complete.

Fixes: 4e0d8463 ("futex: Fix sparc32/m68k/nds32 build regression")
Fixes: 3f2bedab ("futex: Ensure futex_atomic_cmpxchg_inatomic() is present")
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20211203080823.2938839-1-arnd@kernel.org