clk: Fix return value check in oxnas_stdclk_probe()
In case of error, the function syscon_node_to_regmap() returns
ERR_PTR() and never returns NULL. The NULL test in the return
value check should be replaced with IS_ERR().
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn> Acked-by: Neil Armstrong <narmstrong@baylibre.com> Fixes: 0bbd72b4c64f ("clk: Add Oxford Semiconductor OXNAS Standard Clocks") Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>