target-mips: Fix RDHWR on CP0.Count

target-mips: Fix RDHWR on CP0.Count

For RDHWR on the CP0.Count register, env->CP0_Count was being returned.
This value is a delta against the QEMU_CLOCK_VIRTUAL clock, not the
correct current value of CP0.Count. Use cpu_mips_get_count() instead.

Signed-off-by: Alex Smith <alex.smith@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Leon Alrae <leon.alrae@imgtec.com>
Reviewed-by: Leon Alrae <leon.alrae@imgtec.com>
Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>