linux-imx

drm/sti: correctly test devm_ioremap() return

In case of error, the function devm_ioremap_nocache() returns NULL
not ERR_PTR(). The IS_ERR() test in the return value check should
be replaced with NULL test.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>