Fixes for 'Implicit conversion loses integer precision' warnings.

[amubiera]

Since lfs_size_t is defined as uint32_t and not size_t, there are a few warnings for conversion from unsigned long (64-bit) to unsigned int (32-bit) on 64-bit platforms.

lfs.c:288:12 Implicit conversion loses integer precision: 'unsigned long' to 'lfs_size_t' (aka 'unsigned int')
lfs.c:1760:29 Implicit conversion loses integer precision: 'unsigned long' to 'lfs_tag_t' (aka 'unsigned int')

Perhaps lfs_size_t should be defined as size_t instead?

[geky-bot]

Tests passed ✓, Code: 17128 B (+0.0%), Stack: 1448 B (+0.0%), Structs: 812 B (+0.0%)

	Code	Stack	Structs		Coverage
Default	17128 B (+0.0%)	1448 B (+0.0%)	812 B (+0.0%)	Lines	2438/2599 lines (-0.0%)
Readonly	6234 B (+0.0%)	448 B (+0.0%)	812 B (+0.0%)	Branches	1288/1624 branches (-0.0%)
Threadsafe	17980 B (+0.0%)	1448 B (+0.0%)	820 B (+0.0%)		Benchmarks
Multiversion	17200 B (+0.0%)	1448 B (+0.0%)	816 B (+0.0%)	Readed	29000746676 B (+0.0%)
Migrate	18792 B (+0.0%)	1752 B (+0.0%)	816 B (+0.0%)	Proged	1482895246 B (+0.0%)
Error-asserts	17952 B (+0.0%)	1440 B (+0.0%)	812 B (+0.0%)	Erased	1568921600 B (+0.0%)