clk: mmp: pxa1908-apbc: Fix NULL vs IS_ERR() check

The devm_kzalloc() function returns NULL on error, not error pointers.
Fix the check.

Fixes: 51ce5591 ("clk: mmp: Add Marvell PXA1908 APBC driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/d7078eb7-a7d6-4753-b453-8fce15245c34@stanley.mountain


Acked-by: Duje Mihanović <duje.mihanovic@skole.hr>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>