scripts/spelling.txt: drop "sepc" from the misspelling list

The RISC-V architecture has a register named the "Supervisor Exception
Program Counter", or "sepc".  This abbreviation triggers checkpatch.pl's
misspelling detector, resulting in noise in the checkpatch output.  The
risk that this noise could cause more useful warnings to be missed seems
to outweigh the harm of an occasional misspelling of "spec".  Thus drop
the "sepc" entry from the misspelling list.

[akpm@linux-foundation.org: fix existing "sepc" instances, per Joe]
Link: http://lkml.kernel.org/r/20190518210037.13674-1-paul.walmsley@sifive.com


Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>