Reduce the scope of the local err variable in the fm10k_iov_alloc_data
function.

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

[fm10k_iov.c:426]: (style) The scope of the variable 'err' 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>