usb/hcd: Fix a NULL vs IS_ERR() bug in usb_hcd_setup_local_mem()

The devm_memremap() function doesn't return NULL, it returns error
pointers.

Fixes: b0310c2f

 ("USB: use genalloc for USB HCs with local memory")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20190607135709.GC16718@mwanda
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>