docs: correct spelling of "traveling"

While "travelling" isn't incorrect, we generally prefer US english in the
docs, where "traveling" is the common form.

Reviewed-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19139>

docs/drivers/asahi.rst

@@ -43,7 +43,7 @@ Hardware varyings
 
 At an API level, vertex shader outputs need to be interpolated to become
 fragment shader inputs. This process is logically pipelined in AGX, with a value
-travelling from a vertex shader to remapping hardware to coefficient register
+traveling from a vertex shader to remapping hardware to coefficient register
 setup to the fragment shader to the iterator hardware. Each stage is described
 below.