docs: remove apostrophe from uppercased

According to the Merriam-Webster Dictionary, this is the correct way
to spell this word.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29879>

docs/isaspec.rst

@@ -347,7 +347,7 @@ The ``type`` attribute specifies that the input to encoding an instruction
 is a ``struct ir3_instruction *``.  In the case of bitset hierarchies with
 multiple possible leaf nodes, a ``case-prefix`` attribute should be supplied
 along with a function that maps the bitset encode source to an enum value
-with the specified prefix prepended to uppercase'd leaf node name.  I.e. in
+with the specified prefix prepended to uppercased leaf node name.  I.e. in
 this case, "add.f" becomes ``OPC_ADD_F``.
 
 Individual ``<map>`` elements teach the encoder how to map from the encode