As reported in STAR 9001165532, an SLC control reg read (for checking
busy state) right after SLC invalidate command may incorrectly return
NOT busy causing software to NOT spin-wait while operation is underway.
(and for some reason this only happens if L1 cache is also disabled - as
required by IOC programming model)
Suggested workaround is to do an additional Control Reg read, which
ensures the 2nd read gets the right status.
Same fix made in Linux kernel:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c70c473396cbdec1168a6eff60e13029c0916854
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>