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: 596e795569 ("bus: ti-sysc: Add support for software reset")
Signed-off-by: Tony Lindgren <tony@atomide.com>

drivers/bus/ti-sysc.c

@@ -2142,6 +2142,8 @@ static int sysc_reset(struct sysc *ddata)
 		sysc_val = sysc_read_sysconfig(ddata);
 		sysc_val |= sysc_mask;
 		sysc_write(ddata, sysc_offset, sysc_val);
+		/* Flush posted write */
+		sysc_val = sysc_read_sysconfig(ddata);
 	}
 
 	if (ddata->cfg.srst_udelay)