mach-omap2

Fix the size calculation in the verify boot. The header size
should be subtracted from the image size, not be assigned to
the image size.

Fixes: 0830d72b ("arm: am33xx: security: adds auth support for encrypted images")
Signed-off-by: Madan Srinivas <madans@ti.com>
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>