512B is not a correct size to express "512 bytes", and causes a
genimage failure:
ERROR: Invalid size suffix 'B' in '512B'
To express "512 bytes", using just "512" is sufficient. With this
commit, genimage works fine, and we indeed have a 512 bytes unused
partition:
$ fdisk -l output/images/sdcard.img
Disk output/images/sdcard.img: 60 MiB, 62915584 bytes, 122882 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000
Device Boot Start End Sectors Size Id Type
output/images/sdcard.img1 1 1 1 512B 0 Empty
output/images/sdcard.img2 2 524289 524288 256M 83 Linux
Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/88314963
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>