bus: ti-sysc: Flush posted write on enable before reset

The am335x devices started producing boot errors for resetting musb module
in because of subtle timing changes:

Unhandled fault: external abort on non-linefetch (0x1008)
...
sysc_poll_reset_sysconfig from sysc_reset+0x109/0x12
sysc_reset from sysc_probe+0xa99/0xeb0
...

The fix is to flush posted write after enable before reset during
probe. Note that some devices also need to specify the delay after enable
with ti,sysc-delay-us, but this is not needed for musb on am335x based on
my tests.

Reported-by: kernelci.org bot <bot@kernelci.org>
Closes: https://storage.kernelci.org/next/master/next-20230614/arm/multi_v7_defconfig+CONFIG_THUMB2_KERNEL=y/gcc-10/lab-cip/baseline-beaglebone-black.html


Fixes: 596e7955 ("bus: ti-sysc: Add support for software reset")
Signed-off-by: Tony Lindgren <tony@atomide.com>