kmemcheck: Test the full object in kmemcheck_is_obj_initialized()

This is a fix for bug #14845 (bugzilla.kernel.org). The update_checksum()
function in mm/kmemleak.c calls kmemcheck_is_obj_initialised() before scanning
an object. When KMEMCHECK_PARTIAL_OK is enabled, this function returns true.
However, the crc32_le() reads smaller intervals (32-bit) for which
kmemleak_is_obj_initialised() may be false leading to a kmemcheck warning.

Note that kmemcheck_is_obj_initialized() is currently only used by
kmemleak before scanning a memory location.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christian Casteyde <casteyde.christian@free.fr>
Cc: Vegard Nossum <vegardno@ifi.uio.no>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>