[SPARC32]: Fix bogus ramdisk image location check.

This mirrors sparc64 commit 715a0ecc

sparc_ramdisk_image should always be decremented by KERNBASE.

Signed-off-by: Mark Fortescue <mark@mtfhpc.demon.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>