FROMLIST: ARM: kprobes: fix UNPREDICTABLE warnings

GNU as warns twice for this file:
Warning: using r15 results in unpredictable behaviour

via the Arm ARM:
K1.1.1 Overview of the constraints on Armv7 UNPREDICTABLE behaviors

The term UNPREDICTABLE describes a number of cases where the
architecture has a feature that software must not use.

Ard notes:
These are selftests that aim to ensure that kprobe never attempts to
replace the opcodes in question with a probe, but they are not
actually executed, or expected to occur in real code.

Reported-by: kernelci.org bot <bot@kernelci.org>
Suggested-by: Peter Smith <peter.smith@arm.com>
Suggested-by: Renato Golin <rengolin@systemcall.eu>
Suggested-by: David Spickett <david.spickett@linaro.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://github.com/ClangBuiltLinux/linux/issues/1271
Link: https://reviews.llvm.org/D95586
Bug: 141693040
Link: https://lore.kernel.org/linux-arm-kernel/20210211025149.3544593-2-ndesaulniers@google.com/
Change-Id: I42333d7e64a98f739ab13916f61a587143fec7f8