LU-13209 build: SUSE 15 SP2 fix for KBUILD_SRC removed

LU-13209 build: SUSE 15 SP2 fix for KBUILD_SRC removed

Linux v5.2-rc4-45-g051f278e9d81 changed

KBUILD_SRC := $(abs_srctree)
  to
building_out_of_srctree := 1

So adjust the build to handler either case

Test-Parameters: trivial
Cray-bug-id: LUS-8472
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: I385d84cfe0b557f18d17d5732ab943b16b1e1d9c
Reviewed-on: https://review.whamcloud.com/37465
Reviewed-by: Petros Koutoupis <petros.koutoupis@hpe.com>
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Ben Evans <beevans@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>