sh: Ignore R_SH_NONE module relocations.

Some modules may end up with R_SH_NONE relocs with the right combination
of compiler/kernel config (specifically dwarf unwinder), so simply trap
and ignore them instead of letting them get down to the error path.

Reported-by: Carmelo AMOROSO <carmelo.amoroso@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>