x86/pvh: Omit needless clearing of phys_base

Since commit

  d9ec1158 ("x86/boot/64: Use RIP_REL_REF() to assign 'phys_base'")

phys_base is assigned directly rather than added to, so it is no longer
necessary to clear it after use.

Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Message-ID: <20241009160438.3884381-10-ardb+git@google.com>
Signed-off-by: Juergen Gross <jgross@suse.com>