modpost: fix off by one in is_executable_section()

The > comparison should be >= to prevent an out of bounds array
access.

Fixes: 52dc0595 ("modpost: handle relocations mismatch in __ex_table.")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>