kernel-build: No need to run clean and mrproper

The mrproper target cleans everything that clean does, no need to run
both.

Change-Id: I82e588157cf5d7ce50c2483aaefbfddc67d0ff84
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>
1 file changed