leds: bcm6328: Use devm_platform_ioremap_resource() in bcm6328_leds_probe()

Simplify this function implementation by using a known wrapper function.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Pavel Machek <pavel@ucw.cz>