modpost: remove unneeded initializer in section_rel()

This initializer was added to avoid -Wmaybe-uninitialized (gcc) and
-Wsometimes-uninitialized (clang) warnings.

Now that compilers recognize fatal() never returns, it is unneeded.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>