libsparse: Fix odd-sized input files total_blks

If the input file isn't a multiple of block_size, count the trailing
bit as a block in the output, otherwise bootloader will try to write
past the last declared block in the sparse file.

Test: Run sparse_test
Bug: 37339998
Change-Id: Iec143107d15795c6a6f4d3ea7b7515f6f16adcae