fdpic: check that the size returned by kernel_read() is what we asked for

Check that the size of the read returned by kernel_read() is what we asked
for.  If it isn't, then reject the binary as being a badly formatted.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>