Minor libclamav_rust doc and cbindgen typo fix #1936

Job	Run time
check (libclamav, (iana_cctld\|bytecode_api_\|bytecode_hooks\|rijndael\|yara\|inffixed\|inflate\|queue\|n...	25s
check (libfreshclam)	22s
check (clamav-milter)	27s
check (clambc)	27s
check (clamconf)	28s
check (clamd)	24s
check (clamdscan)	27s
check (clamdtop)	24s
check (clamonacc, (c-thread-pool\|fts\|priv_fts))	28s
check (clamscan)	24s
check (clamsubmit)	27s
check (freshclam)	25s
check (libfreshclam)	28s
check (common)	24s
check (sigtool)	26s
check (examples)	26s
check (win32/compat)	25s
	7m 17s

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