isci: fix oem parameter validation on single controller skus

OEM parameters [1] are parsed from the platform option-rom / efi
driver.  By default the driver was validating the parameters for the
dual-controller case, but in single-controller case only the first set
of parameters may be valid.

Limit the validation to the number of actual controllers detected
otherwise the driver may fail to parse the valid parameters leading to
driver-load or runtime failures.

[1] the platform specific set of phy address, configuration,and analog
    tuning values

[stable v3.0+]
Cc: <stable@vger.kernel.org>
Reported-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>