initcalls: Fix m68k build and possible buffer overflow

initcalls: Fix m68k build and possible buffer overflow

This patch fixes a build bug on m68k - gcc decides to emit a call to the
strlen library function, which we don't implement.

More importantly - my previous patch "init: don't lose initcall return
values" (commit bcbfd591cc02617293e240092bc43059a40dca0a) had introduced
potential buffer overflow by wrong calculation of string accumulator
size.

Use strlcat() instead, fixing both bugs.

Many thanks Andreas Schwab and Geert Uytterhoeven for helping
to catch and fix the bug.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>