etc/cppcheck/cppcheck.suppress: Suppress nullPointerOutOfMemory

etc/cppcheck/cppcheck.suppress: Suppress nullPointerOutOfMemory

It causes false positives:

CPPCHECK	.tmp/man/man2/open_by_handle_at.2.d/t_name_to_handle_at.c.lint-c.cppcheck.touch
.tmp/man/man2/open_by_handle_at.2.d/t_name_to_handle_at.c:35:5: warning: inconclusive: If memory allocation fails, then there is a possible null pointer dereference: fhp [nullPointerOutOfMemory]
    fhp->handle_bytes = 0;
    ^
.tmp/man/man2/open_by_handle_at.2.d/t_name_to_handle_at.c:26:17: note: Assuming allocation function fails
    fhp = malloc(fhsize);
                ^
.tmp/man/man2/open_by_handle_at.2.d/t_name_to_handle_at.c:26:17: note: Assignment 'fhp=malloc(fhsize)', assigned value is 0
    fhp = malloc(fhsize);
                ^
.tmp/man/man2/open_by_handle_at.2.d/t_name_to_handle_at.c:35:5: note: Null pointer dereference
    fhp->handle_bytes = 0;
    ^

Signed-off-by: Alejandro Colomar <alx@kernel.org>