KVM: x86: Rename local "ecx" variables to "msr" and "pmc" as appropriate

KVM: x86: Rename local "ecx" variables to "msr" and "pmc" as appropriate

[ Upstream commit ec400f6c2f2703cb6c698dd00b28cfdb8ee5cdcc ]

Rename "ecx" variables in {RD,WR}MSR and RDPMC helpers to "msr" and "pmc"
respectively, in anticipation of adding support for the immediate variants
of RDMSR and WRMSRNS, and to better document what the variables hold
(versus where the data originated).

No functional change intended.

Link: https://lore.kernel.org/r/20250805202224.1475590-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Stable-dep-of: 9d7dfb95da2c ("KVM: VMX: Inject #UD if guest tries to execute SEAMCALL or TDCALL")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>