ice_domain: improve 'max_blocks' computation

The value of 'max_blocks' as currently computed can still be too small
if the number of procs does not divide the number of blocks evenly.

Use the same 'minus one, integer divide, plus one' trick as is done for
the number of blocks in the X and Y directions in order to always
compute a 'max_blocks' value that is large enough.

This estimates the same value for 'max_blocks' as the 'cice_decomp.csh'
script computes:

    @ bx = $nxglob / ${blckx}
    if ($bx * ${blckx} != $nxglob) @ bx = $bx + 1
    @ by = $nyglob / ${blcky}
    if ($by * ${blcky} != $nyglob) @ by = $by + 1

    @ m = ($bx * $by) / ${task}
    if ($m * ${task} != $bx * $by) @ m = $m + 1
    set mxblcks = $m

cicecore/cicedynB/infrastructure/ice_domain.F90

@@ -196,7 +196,7 @@ subroutine init_domain_blocks
    if (my_task == master_task) then
      if (max_blocks < 1) then
        max_blocks=( ((nx_global-1)/block_size_x + 1) *         &
-                    ((ny_global-1)/block_size_y + 1) ) / nprocs
+                    ((ny_global-1)/block_size_y + 1) - 1) / nprocs + 1
        max_blocks=max(1,max_blocks)
        write(nu_diag,'(/,a52,i6,/)') &
          '(ice_domain): max_block < 1: max_block estimated to ',max_blocks