scripts: add spelling.txt for checkpatch.pl

scripts: add spelling.txt for checkpatch.pl

Running the updated checkpatch version with spelling.txt show that
spelling mistakes happen to everyone.

> /target/linux$ fd .*.patch | xargs ../../scripts/checkpatch.pl | rg spell
WARNING: 'usefull' may be misspelled - perhaps 'useful'?
WARNING: 'afecting' may be misspelled - perhaps 'affecting'?
WARNING: 'usefull' may be misspelled - perhaps 'useful'?
WARNING: 'afecting' may be misspelled - perhaps 'affecting'?
WARNING: 'begining' may be misspelled - perhaps 'beginning'?
WARNING: 'superflous' may be misspelled - perhaps 'superfluous'?
WARNING: 'multipe' may be misspelled - perhaps 'multiple'?
WARNING: 'recieves' may be misspelled - perhaps 'receives'?
WARNING: 'retreive' may be misspelled - perhaps 'retrieve'?
WARNING: 'tranfer' may be misspelled - perhaps 'transfer'?
WARNING: 'additonal' may be misspelled - perhaps 'additional'?
WARNING: 'accomodate' may be misspelled - perhaps 'accommodate'?
[...]

Signed-off-by: Paul Spooren <mail@aparcar.org>