selftests/bpf: Fix verifier_bpf_fastcall test

Commit [1] moves percpu data on x86 from address 0x000... to address
0xfff...

Before [1]:

159020: 0000000000030700     0 OBJECT  GLOBAL DEFAULT   23 pcpu_hot

After [1]:

152602: ffffffff83a3e034     4 OBJECT  GLOBAL DEFAULT   35 pcpu_hot

As a result, verifier_bpf_fastcall tests should now expect a negative
value for pcpu_hot, IOW, the disassemble should show "r=" instead of
"w=".

Fix this in the test.

Note that, a later change created a new variable "cpu_number" for
bpf_get_smp_processor_id() [2]. The inlining logic is updated properly
as part of this change, so there is no need to fix anything on the
kernel side.

[1] commit 9d7de2a ("x86/percpu/64: Use relative percpu offsets")
[2] commit 01c7bc5 ("x86/smp: Move cpu number to percpu hot section")
Reported-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20250328193124.808784-1-song@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: liu-song-6

tools/testing/selftests/bpf/progs/verifier_bpf_fastcall.c

@@ -12,7 +12,7 @@ SEC("raw_tp")
 __arch_x86_64
 __log_level(4) __msg("stack depth 8")
 __xlated("4: r5 = 5")
-__xlated("5: w0 = ")
+__xlated("5: r0 = ")
 __xlated("6: r0 = &(void __percpu *)(r0)")
 __xlated("7: r0 = *(u32 *)(r0 +0)")
 __xlated("8: exit")
@@ -704,7 +704,7 @@ SEC("raw_tp")
 __arch_x86_64
 __log_level(4) __msg("stack depth 32+0")
 __xlated("2: r1 = 1")
-__xlated("3: w0 =")
+__xlated("3: r0 =")
 __xlated("4: r0 = &(void __percpu *)(r0)")
 __xlated("5: r0 = *(u32 *)(r0 +0)")
 /* bpf_loop params setup */
@@ -753,7 +753,7 @@ __arch_x86_64
 __log_level(4) __msg("stack depth 40+0")
 /* call bpf_get_smp_processor_id */
 __xlated("2: r1 = 42")
-__xlated("3: w0 =")
+__xlated("3: r0 =")
 __xlated("4: r0 = &(void __percpu *)(r0)")
 __xlated("5: r0 = *(u32 *)(r0 +0)")
 /* call bpf_get_prandom_u32 */