selftests/bpf: fix some typos in selftests

Hi, fix some spelling errors in selftest, the details are as follows:

-in the codes:
	test_bpf_sk_stoarge_map_iter_fd(void)
		->test_bpf_sk_storage_map_iter_fd(void)
	load BTF from btf_data.o->load BTF from btf_data.bpf.o

-in the code comments:
	preample->preamble
	multi-contollers->multi-controllers
	errono->errno
	unsighed/unsinged->unsigned
	egree->egress
	shoud->should
	regsiter->register
	assummed->assumed
	conditiona->conditional
	rougly->roughly
	timetamp->timestamp
	ingores->ignores
	null-termainted->null-terminated
	slepable->sleepable
	implemenation->implementation
	veriables->variables
	timetamps->timestamps
	substitue a costant->substitute a constant
	secton->section
	unreferened->unreferenced
	verifer->verifier
	libppf->libbpf
...

Signed-off-by: Lin Yikai <yikai.lin@vivo.com>
Link: https://lore.kernel.org/r/20240905110354.3274546-1-yikai.lin@vivo.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>