f2fs-tools: optimize the addrs_per_block/inode loop

ADDRS_PER_INODE and ADDRS_PER_BLOCK are macros of a function, and if the
compiler does not optimize the code (-O0 for example), they would be
called in every single loop, which could cause significant performance
drops in some cases.

This scenario has been found before, refer to:
Commit: 1bb669e ("fsck.f2fs: avoid unnecessary recalculation")

To avoid this performance drop as much as possible, I changed the
function to 'inline' definition, which could mitigate such cases in
the future.

Signed-off-by: Wu Bo <wuboo@amazon.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>