target/ppc: avoid int32 multiply overflow in int_helper.c

target/ppc: avoid int32 multiply overflow in int_helper.c

Coverity is not thrilled about the multiply operations being done in
ger_rank8() and ger_rank2(), giving an error like the following:

Integer handling issues  (OVERFLOW_BEFORE_WIDEN)
    Potentially overflowing expression "sextract32(a, 4 * i, 4) *
sextract32(b, 4 * i, 4)" with type "int" (32 bits, signed) is evaluated
using 32-bit arithmetic, and then used in a context that expects an
expression of type "int64_t" (64 bits, signed).

Fix both instances where this occur by adding an int64_t cast in the
first operand, forcing the result to be 64 bit.

Fixes: Coverity CID 1489444, 1489443
Fixes: 345531533f26 ("target/ppc: Implemented xvi*ger* instructions")
Cc: Lucas Mateus Castro (alqotel) <lucas.araujo@eldorado.org.br>
Cc: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Lucas Mateus Castro (alqotel) <lucas.araujo@eldorado.org.br>
Message-Id: <20220602141449.118173-1-danielhb413@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>