partitions/efi: Fix off-by-one error in 'last_lba'
LBAs are numbered starting from zero so the last LBA # would be equal
to total number of blocks minus one.
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>