In old days, Linux created a symlink include/asm -> include/asm-*,
but all the asm headers were moved to arch/*/include/asm, which
is the same for Barebox too.

Remove the bitrotten ignore pattern.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>