soc/intel/{common,apollolake}: Add checks to handle negative values

soc/intel/{common,apollolake}: Add checks to handle negative values

Fix issues reported by coverity scan in the below files.

src/soc/intel/common/block/i2c
	1375440: Improper use of negative value
	1375441: Improper use of negative value
	1375444: Improper use of negative value

src/soc/intel/apollolake/i2c.c
	1375442: Unsigned compared against 0

Change-Id: Ic65400c934631e3dcd3aa664c24cb451616e7f4d
Signed-off-by: Rizwan Qureshi <rizwan.qureshi@intel.com>
Reviewed-on: https://review.coreboot.org/21875
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>