hw/misc: use extract64 instead of 1 << i

hw/misc: use extract64 instead of 1 << i

1 << i is casted to uint64_t while bitwise and with val.
So this value may become 0xffffffff80000000 but only
31th "start" bit is required.
Use the bitfield extract() API instead.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Tigran Sogomonian <tsogomonian@astralinux.ru>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Link: https://lore.kernel.org/r/20241227104618.2526-1-tsogomonian@astralinux.ru
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>