powerpc/fsl_booke: Make calc_cam_sz() static

calc_cam_sz() is used only in fsl_book3e.c, make it static.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a7469848371b2cf5e8f654ec79800e209d88595e.1660919200.git.christophe.leroy@csgroup.eu