x86/paravirt: Use XOR r32,r32 to clear register in pv_vcpu_is_preempted()

x86/paravirt: Use XOR r32,r32 to clear register in pv_vcpu_is_preempted()

x86_64 zero extends 32bit operations, so for 64bit operands, XOR r32,r32 is
functionally equal to XOR r64,r64, but avoids a REX prefix byte when legacy
registers are used.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Acked-by: Alexey Makhalov <alexey.makhalov@broadcom.com>
Link: https://patch.msgid.link/20260114211948.74774-2-ubizjak@gmail.com