cmd/compile: fix arg to getcallerpc
cmd/compile: fix arg to getcallerpc

getcallerpc's arg needs to point to the first argument slot.
I believe this bug was introduced by Michel's itab changes
(specifically https://go-review.googlesource.com/c/20902).

Fixes #15145

Change-Id: Ifb2e17f3658e2136c7950dfc789b4d5706320683
Reviewed-on: https://go-review.googlesource.com/21931
Reviewed-by: Michel Lespinasse <6a4cf9207bb95b1a4cf1be22c2e93f8b38036f65@google.com>

josharian/go,CAFxX/go,ganboing/go-esx,theif519/go,josharian/go,akutz/go,ganboing/go-esx,suncycheng/go,polyverse-security/go,vanloswang/go,ganboing/go-esx,derekmarcotte/go,polyverse-security/go,suncycheng/go,linux-on-ibm-z/go,4ad/go,golang/go,momchil-velikov/go,codestation/go,Cofyc/go,cloudflare/go,linux-on-ibm-z/go,momchil-velikov/go,suncycheng/go,4ad/go,suncycheng/go,akutz/go,vanloswang/go,theif519/go,linux-on-ibm-z/go,momchil-velikov/go,cloudflare/go,akutz/go,theif519/go,ImJasonH/go,cloudflare/go,4ad/go,derekmarcotte/go,codestation/go,vanloswang/go,vsekhar/elastic-go,Cofyc/go,CAFxX/go,Cofyc/go,suncycheng/go,ganboing/go-esx,goodlang/good,goodlang/good,theif519/go,cloudflare/go,golang/go,linux-on-ibm-z/go,vsekhar/elastic-go,Cofyc/go,derekmarcotte/go,polyverse-security/go,CAFxX/go,ImJasonH/go,vsekhar/elastic-go,akutz/go,josharian/go,akutz/go,nawawi/go,polyverse-security/go,nawawi/go,Cofyc/go,theif519/go,nawawi/go,polyverse-security/go,CAFxX/go,linux-on-ibm-z/go,nawawi/go,josharian/go,josharian/go,linux-on-ibm-z/go,CAFxX/go,momchil-velikov/go,theif519/go,derekmarcotte/go,theif519/go,nawawi/go,akutz/go,goodlang/good,linux-on-ibm-z/go,suncycheng/go,codestation/go,momchil-velikov/go,momchil-velikov/go,ganboing/go-esx,cloudflare/go,golang/go,suncycheng/go,polyverse-security/go,vanloswang/go,vsekhar/elastic-go,linux-on-ibm-z/go,vanloswang/go,josharian/go,goodlang/good,4ad/go,Cofyc/go,vanloswang/go,codestation/go,momchil-velikov/go,ganboing/go-esx,vanloswang/go,goodlang/good,ImJasonH/go,goodlang/good,goodlang/good,ImJasonH/go,vsekhar/elastic-go,vsekhar/elastic-go,golang/go,vsekhar/elastic-go,4ad/go,Cofyc/go,goodlang/good,vanloswang/go,cloudflare/go,cloudflare/go,theif519/go,akutz/go,ganboing/go-esx,polyverse-security/go,momchil-velikov/go,derekmarcotte/go,codestation/go,4ad/go,golang/go,josharian/go,ImJasonH/go,ImJasonH/go,derekmarcotte/go,golang/go,codestation/go,4ad/go,suncycheng/go,nawawi/go,derekmarcotte/go,polyverse-security/go,4ad/go,ganboing/go-esx,vsekhar/elastic-go,codestation/go,nawawi/go,derekmarcotte/go,akutz/go,nawawi/go,golang/go,CAFxX/go,cloudflare/go,christopher-henderson/Go,josharian/go,golang/go,Cofyc/go,CAFxX/go,CAFxX/go,codestation/go,ImJasonH/go,ImJasonH/go