ice: Rework ice_ena_msix_range

The current implementation of ice_ena_msix_range is difficult to read
and has subtle issues. This patch reworks the said function for
clarity and correctness.

More specifically,

1. Add more checks to bail out of 'needed' is greater than 'v_left'.

2. Simplify fallback logic

3. Do not set pf->num_avail_sw_msix in ice_ena_msix_range as it
   gets overwritten by ice_init_interrupt_scheme.

Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>