target/arm: Use correct variable for setting 'max' cpu's ID_AA64DFR0

target/arm: Use correct variable for setting 'max' cpu's ID_AA64DFR0

In aarch64_max_initfn() we update both 32-bit and 64-bit ID
registers.  The intended pattern is that for 64-bit ID registers we
use FIELD_DP64 and the uint64_t 't' register, while 32-bit ID
registers use FIELD_DP32 and the uint32_t 'u' register.  For
ID_AA64DFR0 we accidentally used 'u', meaning that the top 32 bits of
this 64-bit ID register would end up always zero.  Luckily at the
moment that's what they should be anyway, so this bug has no visible
effects.

Use the right-sized variable.

Fixes: 3bec78447a958d481991
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20200423110915.10527-1-peter.maydell@linaro.org