devm_memremap: Fix error value when memremap failed

devm_memremap: Fix error value when memremap failed

devm_memremap() returns an ERR_PTR() value in case of error.
However, it returns NULL when memremap() failed.  This causes
the caller, such as the pmem driver, to proceed and oops later.

Change devm_memremap() to return ERR_PTR(-ENXIO) when memremap()
failed.

Signed-off-by: Toshi Kani <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: <[email protected]>
Reviewed-by: Ross Zwisler <[email protected]>
Signed-off-by: Dan Williams <[email protected]>