checkpatch: improve seq_print->seq_puts suggestion

Improve the format specifier test by removing any %% before looking for
any remaining % format specifier.

Signed-off-by: Heba Aamer <heba93aamer@gmail.com>
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>