powerpc/mm: Drop VM_BUG_ON in get_region_id()

We call get_region_id() without validating the ea value. That means
with a wrong ea value we hit the BUG as below.

  kernel BUG at arch/powerpc/include/asm/book3s/64/hash.h:129!
  Oops: Exception in kernel mode, sig: 5 [#1]
  LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
  CPU: 0 PID: 3937 Comm: access_tests Not tainted 5.1.0
  ....
  NIP [c00000000007ba20] do_slb_fault+0x70/0x320
  LR [c00000000000896c] data_access_slb_common+0x15c/0x1a0

Fix this by removing the VM_BUG_ON. All callers make sure the returned
region id is valid and error out otherwise.

Fixes: 0034d395 ("powerpc/mm/hash64: Map all the kernel regions in the same 0xc range")
Reported-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/book3s/64/hash.h

@@ -122,11 +122,9 @@ static inline int get_region_id(unsigned long ea)
 	if (ea < H_KERN_VIRT_START)
 		return LINEAR_MAP_REGION_ID;
 
-	VM_BUG_ON(id != 0xc);
 	BUILD_BUG_ON(NON_LINEAR_REGION_ID(H_VMALLOC_START) != 2);
 
 	region_id = NON_LINEAR_REGION_ID(ea);
-	VM_BUG_ON(region_id > VMEMMAP_REGION_ID);
 	return region_id;
 }