staging: media: atomisp: kmap() can't fail

There's no need to check kmap() return value because it won't fail.
If it's highmem mapping, it will receive virtual address
or a new one; if it's lowmem, all kernel pages are already being mapped.

(Thanks to Jan Kara for explanations)

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>