[SPARC64]: Fix inconsistent .section usage in lib/

A few places missed the "a" specifier for the __ex_table section. Add
these so we avoid generation an additional section at link time.

Latest modpost would otherwise complain like this:

WARNING: vmlinux.o (__ex_table.2): section name inconsistency.
(.[number]+) following section name.
Did you forget to use "ax"/"aw" in a .S file?
Note that for example <linux/init.h> contains
section definitions for use in .S files.
WARNING: vmlinux.o (__ex_table.4): section name inconsistency.
(.[number]+) following section name.
Did you forget to use "ax"/"aw" in a .S file?
Note that for example <linux/init.h> contains
section definitions for use in .S files.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>