unnecessary calculation in function s_get_next_block of salloc.c

[Changqing-JING]

static char* s_get_next_block( char* ptr )
{
return ( char* )( ( ( u32 )ptr & 0x7FFFFFFF ) << DYN_SIZE_MULT_SHIFT );
}

This function is made of two calculations:

1. set the highest bit as 0.
2. left shift 3 bits

But if a number is left shift for 3 bits, the highest bit will be overflow. So the result is independent of whether the highest bit is 0 or 1. The first calculation can be removed.