udf: remove reporting loc in debug output

clang build fails with
fs/udf/partition.c:86:28: error: variable 'loc' is uninitialized when used here [-Werror,-Wuninitialized]
                          sb, block, partition, loc, index);
                                                ^~~

loc is now only known when bh is valid. So remove reporting loc in debug
output.

Fixes: 4215db46 ("udf: Use udf_bread() in udf_get_pblock_virt15()")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: "kernelci.org bot" <bot@kernelci.org>
Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>