fm10k: reduce the scope of the local i variable

Reduce the scope of the local loop variable in the
fm10k_check_hang_subtask function.

This was detected by cppcheck and resolves the following warning
produced by that tool:

[driver/fm10k_pci.c:852]: (style) The scope of the variable 'i' can be
reduced.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>