[MemProf][NFC] Compute SHADOW_ENTRY_SIZE from MEM_GRANULARITY and SHA… (#80589)

…DOW_SCALE

As MEM_GRANULARITY represents the size of memory block mapped to a
single shadow entry, and SHADOW_SCALE represents the scale of shadow
mapping, so the single shadow entry size can be computed as
(MEM_GRANULARITY >> SHADOW_SCALE).

This patch replaces the hardcoded SHADOW_ENTRY_SIZE with
(MEM_GRANULARITY >> SHADOW_SCALE).