doc: use appropriate type to describe return value
doc: use appropriate type to describe return value

Fixes #19223.

Change-Id: I4cc8e81559a1313e1477ee36902e1b653155a888
Reviewed-on: https://go-review.googlesource.com/37374
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

cloudflare/go,codestation/go,CAFxX/go,cloudflare/go,akutz/go,CAFxX/go,josharian/go,akutz/go,golang/go,Cofyc/go,nawawi/go,akutz/go,ImJasonH/go,vsekhar/elastic-go,derekmarcotte/go,linux-on-ibm-z/go,codestation/go,polyverse-security/go,golang/go,cloudflare/go,golang/go,josharian/go,derekmarcotte/go,ImJasonH/go,derekmarcotte/go,linux-on-ibm-z/go,CAFxX/go,derekmarcotte/go,linux-on-ibm-z/go,derekmarcotte/go,vsekhar/elastic-go,akutz/go,cloudflare/go,cloudflare/go,polyverse-security/go,codestation/go,Cofyc/go,linux-on-ibm-z/go,ImJasonH/go,CAFxX/go,josharian/go,vsekhar/elastic-go,nawawi/go,akutz/go,codestation/go,Cofyc/go,golang/go,CAFxX/go,Cofyc/go,akutz/go,derekmarcotte/go,derekmarcotte/go,polyverse-security/go,polyverse-security/go,vsekhar/elastic-go,ImJasonH/go,linux-on-ibm-z/go,akutz/go,golang/go,codestation/go,vsekhar/elastic-go,derekmarcotte/go,vsekhar/elastic-go,ImJasonH/go,Cofyc/go,polyverse-security/go,ImJasonH/go,ImJasonH/go,codestation/go,akutz/go,josharian/go,golang/go,Cofyc/go,polyverse-security/go,Cofyc/go,linux-on-ibm-z/go,nawawi/go,CAFxX/go,josharian/go,nawawi/go,CAFxX/go,polyverse-security/go,christopher-henderson/Go,golang/go,linux-on-ibm-z/go,nawawi/go,linux-on-ibm-z/go,josharian/go,nawawi/go,Cofyc/go,golang/go,ImJasonH/go,cloudflare/go,cloudflare/go,vsekhar/elastic-go,codestation/go,nawawi/go,cloudflare/go,polyverse-security/go,nawawi/go,josharian/go,vsekhar/elastic-go,codestation/go,CAFxX/go,josharian/go