clk: ti: fix linker error with !SOC_OMAP4

When none of the OMAP4-generation SoCs are enabled, we run into a link
error for am43xx/am43xx:

drivers/clk/ti/dpll.o: In function `of_ti_am3_dpll_x2_setup':
dpll.c:(.init.text+0xd8): undefined reference to `clkhwops_omap4_dpllmx'

This is easily fixed by adding another #ifdef.

While looking at the code, I also spotted another problem with the
assignment of hw_ops variable that is not used again later. I'm
changing this to setting clk_hw->ops instead, which I guess is what
was intended here.

Fixes: 473adbf4 ("clk: ti: dpll44xx: fix clksel register initialization")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Tero Kristo <t-kristo@ti.com>
[sboyd@codeaurora.org: Replaced fixes tag with correct one]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>