scripts/spelling.txt: add syfs/sysfs pattern

There are a few cases in the tree where "sysfs" is misspelled as "syfs".

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.ne>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Xiong <xndchn@gmail.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Chris Paterson <chris.paterson2@renesas.com>
Cc: Luca Ceresoli <luca@lucaceresoli.net>
Link: http://lkml.kernel.org/r/20200218152010.27349-1-j.neuschaefer@gmx.net


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>