tools: kwbimage: Fix generating, verifying and extracting SATA kwbimage

Despite the official specification, Marvell BootROM does not interpret
srcaddr from SATA image as number of sectors the beginning of the hard
drive, but as number of sectors relative to the main header.

The main header is stored at absolute sector number 1. So do not add or
subtract it when calculating with relative offsets to the main header.

Fixes: 501a54a2 ("tools: kwbimage: Fix generation of SATA, SDIO and PCIe images")
Fixes: 5c61710c ("tools: kwbimage: Properly set srcaddr in kwbimage v0")
Fixes: e0c243c3 ("tools: kwbimage: Validate data checksum of v1 images")
Fixes: aa6943ca ("kwbimage: Add support for extracting images via dumpimage tool")
Signed-off-by: Pali Rohár <pali@kernel.org>