FRV: Don't attempt to #include <linux/blk.h> as it doesn't exist

Stop the FRV arch from attempting to #include <linux/blk.h> as it doesn't
exist.

Reported-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>