kbuild: fix kernel/bounds.c 'W=1' warning

kbuild: fix kernel/bounds.c 'W=1' warning

Building any configuration with 'make W=1' produces a warning:

kernel/bounds.c:16:6: warning: no previous prototype for 'foo' [-Wmissing-prototypes]

When also passing -Werror, this prevents us from building any other files.
Nobody ever calls the function, but we can't make it 'static' either
since we want the compiler output.

Calling it 'main' instead however avoids the warning, because gcc
does not insist on having a declaration for main.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnd Bergmann <[email protected]>
Reported-by: Kieran Bingham <[email protected]>
Reviewed-by: Kieran Bingham <[email protected]>
Cc: David Laight <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>