Fixes compile errors for ddr4 a38x in U-Boot

[mibodhi]

Upstream U-Boot project contains some a38x patch which fixes compile errors for ddr4 a38x.

• Modify mv_ddr4_calibration_validate function body to match function header.
• Convert floating point operations to integer operations.

[pali]

@kostapr Could you look at this PR?

[pali]

@kostapr Thanks!

Anyway, could you please synchronize patches between internal SDK version and this github version?