bus: ti-sysc: Add break in switch statement in sysc_init_soc()

After commit a6d90e9f ("bus: ti-sysc: AM3: RNG is GP only"), clang
with -Wimplicit-fallthrough enabled warns:

drivers/bus/ti-sysc.c:2958:3: warning: unannotated fall-through between
switch labels [-Wimplicit-fallthrough]
                default:
                ^
drivers/bus/ti-sysc.c:2958:3: note: insert 'break;' to avoid
fall-through
                default:
                ^
                break;
1 warning generated.

Clang's version of this warning is a little bit more pedantic than
GCC's. Add the missing break to satisfy it to match what has been done
all over the kernel tree.

Fixes: a6d90e9f ("bus: ti-sysc: AM3: RNG is GP only")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>