x86/pv-shim: fix grant table operations for 32-bit guests

x86/pv-shim: fix grant table operations for 32-bit guests

When switching to call the shim functions from the normal handlers, the
compat_grant_table_op() function was omitted, leaving it calling the
real grant table operations in !PV_SHIM_EXCLUSIVE builds. This leaves a
32-bit shim guest failing to set up its real grant table with the parent
hypervisor.

Fixes: e7db635f4428 ("x86/pv-shim: Don't modify the hypercall table")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>