ice: Re-organizes reqstd/avail {R, T}XQ check/code for efficiency

If user has explicitly requested the number of {R,T}XQs, then it is
unnecessary to get the count of already available {R,T}XQs from the
PF avail_{r,t}xqs bitmap. This value will get overridden by user specified
value in any case.

Re-organize this code for improving the flow, readability and efficiency.
This scope of improvement was found during the review of the ICE driver
code.

Fixes: 87324e74 ("ice: Implement ethtool ops for channels")
Cc: intel-wired-lan@lists.osuosl.org
Tested-by: Tony Brelinski <tonyx.brelinski@intel.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>