mtd: cfi_cmdset_0002: only check errors when ready in cfi_check_err_status()

mtd: cfi_cmdset_0002: only check errors when ready in cfi_check_err_status()

BugLink: https://bugs.launchpad.net/bugs/1861090
commit 72914a8cff7e1d910c58e125e15a0da409e3135f upstream.

Cypress S26K{L|S}P{128|256|512}S datasheet says that the error bits in
the status register are only valid when the "device ready" bit 7 is set.
Add the check for the device ready bit in cfi_check_err_status() as that
function isn't always called with this bit set.

Fixes: 4844ef80305d ("mtd: cfi_cmdset_0002: Add support for polling status register")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>