kldxref: Appease a Coverity warning

While parsing .dynamic, nsym is set when parsing the symbol table from
.dynsym.  That parsing also sets ef->ef_symtab to a non-NULL value.
The value of nsym isn't validated until after a check for
ef->ef_symtab being NULL, so nsym always has a valid value when it is
read.  However, that chain of events is a bit much for static analysis
to follow, so initialize nsym to 0 before parsing sections to quiet
the warning.

Reported by:	Coverity Scan
CID:		1532339
Sponsored by:	DARPA

usr.sbin/kldxref/ef.c

@@ -361,6 +361,7 @@ ef_parse_dynamic(elf_file_t ef, const GElf_Phdr *phdyn)
 		goto out;
 	}
 
+	nsym = 0;
 	for (i = 0; i < nshdr; i++) {
 		switch (shdr[i].sh_type) {
 		case SHT_HASH: