kexec: remove unnecessary test in kimage_alloc_crash_control_pages()

Transforming PFN(Page Frame Number) to struct page is never failure, so we
can simplify the code logic to do the image->control_page assignment
directly in the loop, and remove the unnecessary conditional judgement.

Signed-off-by: Minfei Huang <mnfhuang@gmail.com>
Acked-by: Dave Young <dyoung@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Cc: Simon Horman <horms@verge.net.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>