dynamic_debug: remove wrong error message

parse_lineno() returns either negative error code or zero.  We don't
need to print something here because if parse_lineno fails it will print
error message.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>