[llvm] [Mips] Fix fast isel for i16 bswap. (PR #103398)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `openmp-offload-libc-amdgpu-runtime` running on `omp-vega20-1` while building `llvm` at step 10 "Add check check-offload".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/73/builds/3940

Here is the relevant piece of the build log for the reference:
```
Step 10 (Add check check-offload) failure: 1200 seconds without output running [b'ninja', b'-j 32', b'check-offload'], attempting to kill
...
PASS: libomptarget :: x86_64-pc-linux-gnu-LTO :: offloading/bug47654.cpp (848 of 858)
PASS: libomptarget :: x86_64-pc-linux-gnu-LTO :: offloading/bug50022.cpp (849 of 858)
PASS: libomptarget :: x86_64-pc-linux-gnu-LTO :: offloading/test_libc.cpp (850 of 858)
PASS: libomptarget :: x86_64-pc-linux-gnu-LTO :: offloading/bug53727.cpp (851 of 858)
PASS: libomptarget :: x86_64-pc-linux-gnu-LTO :: offloading/wtime.c (852 of 858)
PASS: libomptarget :: x86_64-pc-linux-gnu :: offloading/bug49021.cpp (853 of 858)
PASS: libomptarget :: x86_64-pc-linux-gnu :: offloading/std_complex_arithmetic.cpp (854 of 858)
PASS: libomptarget :: x86_64-pc-linux-gnu-LTO :: offloading/complex_reduction.cpp (855 of 858)
PASS: libomptarget :: x86_64-pc-linux-gnu-LTO :: offloading/bug49021.cpp (856 of 858)
PASS: libomptarget :: x86_64-pc-linux-gnu-LTO :: offloading/std_complex_arithmetic.cpp (857 of 858)
command timed out: 1200 seconds without output running [b'ninja', b'-j 32', b'check-offload'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1232.540061

```

https://github.com/llvm/llvm-project/pull/103398