[gdb/contrib] Add SME to codespell-ignore-words.txt

Ignore the following codespell detection:
...
$ codespell --config gdbserver/setup.cfg gdbserver
gdbserver/linux-aarch64-low.cc:827: SME ==> SAME, SEME, SOME, SMS
...
by adding SME to codespell-ignore-words.txt.

gdb/contrib/codespell-ignore-words.txt

diff --git a/gdb/contrib/codespell-ignore-words.txt b/gdb/contrib/codespell-ignore-words.txt
index a8287f7..2b9d878 100644
--- a/gdb/contrib/codespell-ignore-words.txt
+++ b/gdb/contrib/codespell-ignore-words.txt
@@ -1,3 +1,4 @@
 configury
 invokable
 useable
+SME