internal/cpu: fix style nit in variable name
internal/cpu: fix style nit in variable name

Consistent with similar change of style in the crypto repository:
http://golang.org/cl/43511

Change-Id: Ib158c52a2649dcbbe9eb92f2bdb9d289e0dcc7bf
Reviewed-on: https://go-review.googlesource.com/53474
Reviewed-by: Han-Wen Nienhuys <3269a793d567baa2fa5b041e3e5e0a5039790a2f@google.com>
Reviewed-by: Avelino <8efd86fb78a56a5145ed7739dcb00c78581c5375@avelino.xxx>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/go,cloudflare/go,golang/go,CAFxX/go,codestation/go,akutz/go,nawawi/go,polyverse-security/go,Cofyc/go,CAFxX/go,josharian/go,CAFxX/go,Cofyc/go,codestation/go,josharian/go,codestation/go,CAFxX/go,polyverse-security/go,akutz/go,golang/go,nawawi/go,golang/go,codestation/go,polyverse-security/go,nawawi/go,cloudflare/go,akutz/go,CAFxX/go,polyverse-security/go,CAFxX/go,golang/go,akutz/go,codestation/go,Cofyc/go,codestation/go,polyverse-security/go,codestation/go,josharian/go,josharian/go,cloudflare/go,akutz/go,CAFxX/go,cloudflare/go,golang/go,cloudflare/go,josharian/go,cloudflare/go,Cofyc/go,akutz/go,akutz/go,josharian/go,nawawi/go,christopher-henderson/Go,polyverse-security/go,CAFxX/go,Cofyc/go,Cofyc/go,cloudflare/go,cloudflare/go,golang/go,nawawi/go,josharian/go,polyverse-security/go,codestation/go,nawawi/go,josharian/go,nawawi/go,Cofyc/go,polyverse-security/go,akutz/go,nawawi/go,Cofyc/go,golang/go