Use the mem_is_zero() helper where possible.

Conversion done using cocci:

| @@
| expression PTR;
| expression SIZE;
| @@
|
|   <...
| (
| - memchr_inv(PTR, 0, SIZE) == NULL
| + mem_is_zero(PTR, SIZE)
| |
| - !memchr_inv(PTR, 0, SIZE)
| + mem_is_zero(PTR, SIZE)
| |
| - memchr_inv(PTR, 0, SIZE)
| + !mem_is_zero(PTR, SIZE)
| )
|   ...>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240814100035.3100852-2-jani.nikula@intel.comSigned-off-by: Jani Nikula <jani.nikula@intel.com>