[MTD] [NOR] Prevent erase command invocation on suspended chip

while running stress tests we have met cfi_cmdset_0001.c driver issue.
Working on multipartitional devices with erase suspend on write
feature enabled it is possible to get erase operation invoked on chip
with suspended erase. get_chip() looses information about earlier
suspended erase and new erase operation gets issued. New erase
operations report successful completion, but blocks remain dirty
causing, for example, JFFS2 error messages like:

...
Newly-erased block contained word 0x20031985 at offset 0x00200000
Newly-erased block contained word 0x20031985 at offset 0x00280000
Newly-erased block contained word 0x20031985 at offset 0x00240000
...

The patch below fixes that issue.

Signed-off-by: Alexander Belyakov <alexander.belyakov@intel.com>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>