ppc/pnv: use a do-while() loop in pnv_phb3_translate_tve()

ppc/pnv: use a do-while() loop in pnv_phb3_translate_tve()

The 'taddr' variable is left unintialized, being set only inside the
"while ((lev--) >= 0)" loop where we get the TCE address. The 'lev' var
is an int32_t that is being initiliazed by the GETFIELD() macro, which
returns an uint64_t.

For a human reader this means that 'lev' will always be positive or zero.
But some compilers may beg to differ. 'lev' being an int32_t can in theory
be set as negative, and the "while ((lev--) >= 0)" loop might never be
reached, and 'taddr' will be left unitialized. This can cause phb3_error()
to use 'taddr' uninitialized down below:

if ((is_write & !(tce & 2)) || ((!is_write) && !(tce & 1))) {
    phb3_error(phb, "TCE access fault at 0x%"PRIx64, taddr);

A quick way of fixing it is to use a do/while() loop. This will keep the
same semanting as the existing while() loop does and the compiler will
understand that 'taddr' will be initialized at least once.

Suggested-by: Matheus K. Ferst <matheus.ferst@eldorado.org.br>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/573
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220127122234.842145-2-danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>